This information is lifted pretty much verbatim from a posting by Michael Colao on the uk-freeforms e-group, and as such is his opinions and experiences of the relevant suppliers.
This information is now quite old - the original post by Michael was back in 2004. I have updated the links where necessary and removed redundant entries - but information about opening times, prices and payment options is probably not still current.
If anyone has any other information about costume hire - either in London or elsewhere, please let me know.
This is not meant to be an exhaustive list, and I definitely focus on Central London (with one exception). I have listed them roughly in order of price/features. As a rule, better costumes means more money, but not always, and full details are in the text.
A reasonable place to start is the South London Theatre:
This is an amateur dramatic society located near the West Norwood railway station. Visiting their costume racks is a lottery. They have a mixed range of odd stuff on the racks. They may well have exactly what you need in your size, they might not. It all depends on what shows they have run before, and what size those actors were. They are open on TUESDAY NIGHTS ONLY and are staffed by volunteers. They rent by the week and they are VERY inexpensive (say £12). They will want you to pay by cheque if you rent from them, and they will take two cheques, one as a deposit. They are well worth checking out, as if they have what you want it's great, and very cheap, and if not, you are not out much.
This is on Camden High Street very near the Camden Town tube. This is one of the cheaper of the fully professional hire places I found in central London (£30 - £35). This is almost as much of a crapshoot as SLT. You can see pictures of all of their costumes on line, but they have (as a rule), one of each. So, for example, if you see that you like say the Victorian Brown suit (E96), they have one of those (38-42 chest). If you fit it, great, if not, pity. The shop does have a wide range of costume accessories, hats, badges, wigs canes, etc. ranging from the outrageously tacky to the merely mildly tacky. It was hear that I found a Deputy Sheriff's badge for Jon Cloutman for Appalachian Wedding after he complained that he could find Sheriff's badges everywhere, but no deputy badges.
This is one of the largest fancy dress outfits in London, with two large stores, one on Grey's Inn Road near Chancery Lane Tube and the other near Old Street Tube in the City. They specialise in the Corporate Fancy Dress Party. They are ideal if you need a Santa Outfit, a Bunny Rabbit suit, a stereotypical pirate outfit, etc.
Their costumes are not particularly period-accurate, and they are not particularly cheap (say £85). On the positive side, they will be able to get you a costume, on no or short notice, and the staff there do understand and appreciate period costume, even if they cannot rent you one. I was quite struck by the way in which the costume assistants there went out of their way to attempt to fake the correct look. On the positive side, they rent by the Costume, not by the piece. So if you need a cane, cloak, change of shirt (say for a weekend long freeform), they will not charge extra. Nonetheless, for what they charge, I felt strongly that one can do better in London.
Angels advertises itself as "The largest and most comprehensive costume company in the world". Founded in 1840, it specialises in Professional costuming. They have a 150,000 square foot warehouse in Hendon that contains almost any article of costume that you can imagine. You are not allowed to go there. Their main business is the costuming of films, and they have supplied costumes to Master and Commander, Gangs of New York, Black Hawk Down, Elizabeth, Captain Corelli's Mandolin, The Mummy Returns, Titanic, Shakespeare in Love, Harry Potter, and others. I repeat, you are not allowed to go to Hendon. You are allowed to go to Angel's Fancy Dress which is located at 119 Shaftesbury Avenue just off Charing Cross Road. The shop closes at 17:30, but you absolutely have to be in no later than 16:30 or you will not be seen. Renting here is an experience. You will be assigned a dresser, who will bring you various garments, and make suggestions as to the way to wear various items. Allow yourself lots of time. For something that needs to be right, they can and will order stock from their Hendon warehouse (which takes several days to show up). So if you elect to rent from Angels, you may wish more than one fitting, but you will get something that is as period-accurate as possible. This is another outfit that will hire by the costume, not by the piece, so if you need flourishes like opera capes, etc. they are all included in the price (which is about £95). This is dear (though not much dearer than the vastly inferior Mad World), but the quality is superb, and the two dressers that I met there were both extremely expert. By the way, trying on a costume with a dresser is an experience in itself. I would recommend Angels, but they are expensive. Even if you are not planning to rent, this is a useful place to window shop.
There is now online access to the Angels collection at FancyDress.com
Now this is a place that is frockage heaven. The The Royal National Theatre costume department make costumes for the roughly twenty plays a year that are put on by the NT. After the show, the costumes go to the costume racks where they are frequently rented by everyone from school groups to films (costumes were supplied to Braveheart, Rob Roy, The Madness of King George, King Lear (BBC), Jude, The Crucible, and others). They do rent to individuals, but you need to make an appointment to go and see them. They are open by appointment Monday to Friday 10am- 1pm and 2pm-6pm. If you know where the National Theatre is, well it's not there. Rather it is at their workshops on Brixton Road near Oval Tube. What you do: Simply call them up, tell them that you wish to rent for a corporate or private function and make an appointment. When you get there, you will be shown into the racks, be given a 5 minute introduction, and that's it. You are left loose in the costume racks to explore. They have everything from Ancient Egyptian to Science Fiction largely arranged chronologically, and you can try on whatever you want. It is frockage heaven. Some of the interior pieces (such as waistcoats) were clearly designed for theatrical use, with a highly elaborate and decorated front, and a much plainer (or almost nonexistent) back. There is an astonishing range here, though it must be noted that they rent per piece. So to rent one shirt is £5, two shirts is £10 , a frockcoat is £30 - £35 and so on. Expect to pay roughly £95 for a full Victorian outfit, but when you add opera capes, and costume changes this will be more expensive than even Angels. The fact that they rent per piece however can work to your advantage. If you have most of an outfit, but are short the right hat, or the right cape, or just that trimming that will make the outfit soar, then this can be a very effective and not all that expensive option to add the right flourishes. One last point relates to their rental process. Spend the day picking the items you want and take them in to the little office there. They will examine the items and then NOT give you a final quote NOR allow you to take them away. Rather they will begin a one-two day paperwork process that will result in a final quote roughly 24 hours after you have selected the items, and then you need to make a second trip down there to pick them up.
Sigh. But a day in the Wardrobe racks really is frockage heaven.