Everyone attending the event must wear sailor suit whites. Obviously the whole point of the event is that all shipmates are all dressed the same or very similar so please do make the effort. With these sort of events, you typically get out of the event what you put in, so don’t hold back. You will not regret it.
The classic sailor suit is ably demonstrated by this US Navy sailor:
Two good options for hiring sailor outfits in central London are:
Mad World Fancy Dress
(69-85 Tabernacle Street, London EC2A 4BA and 441 The Strand, London WC2N 4HZ)
Angels Fancy Dress Shop
(119 Shaftesbury Avenue, London WC2H 8AE)
Both shops also have online stores where you can buy a sailor outfit.
For those who want to retain their outfit for posterity (and next year!) there are several examples online of where to buy the outfits from.
For example, Angels Fancy Dress Shop has this sailor costume for £35:
Party Delights has a sailor costume for £19:
Or you can always try eBay.
There are several female versions of the classic white sailor outfit on both of these websites.
One word of caution. As the event is taking place in London where the weather can be temperamental, we advise you to check the weather forecast in advance. Please bear this in mind and dress appropriately for warmth and potentially rain. We suggest wearing some layers underneath your sailor suit.