- We got married this year (Southwark Cathedral) then took our guests down the river to the National Liberal Club in Westminster - would highly recommend them! Ours was similar sized reception to yours, and they have 2 amazing rooms (one for dinner, and bar, and seperate one for dancing, with loads of lounge space). They also have a fantastic terrace overlooking the river. Not SE1 - but brilliant nonetheless!
- In SE1, we looked into: Shakespeare's Globe (worked out slightly over-budget, and also didn't think it would work in May, but I thought it would be a pretty awesome winter wedding venue); Glaziers Hall (seemed a bit soulless inside, and the actual hall didn't overlook the river - but great room for drinks beforehand); Royal Festival Hall - they have a great room near the top, with an area for bar and coats, and roof garden. Fabulous views.
Hope this helps! Have fun planning, i loved the whole experience, as you can probably tell! :)
I would endorse the Delfina, but you will not be able to do your own catering there nor at Glaziers, Blue Print etc. I am a local event organiser, so know many unusual venues, but most have tied catering arrangements. If you get really stuck or need some intros private message me.
Not in SE1, but close by - my husband and I got married at The Barbican Conservatory in May 2008. Cannot recommend highly enough, very capable wedding planner there (Alex - not sure if she's still around now) and very reasonable food/drink packages. We weren't going to look there originally as Barbican can appear a bit of a concrete jungle (plus my husband had memories of doing exams there!) but once inside the conservatory we didn't look back, it's an absolutely magical venue.