Are there any networking opportunities for startups (primarily internet entrepreneurs) in the UK - or more specifically, London?
Since we are mostly bootstrapping and therefore need to keep costs down, we are mostly interested in free events - or events that have a nominal fee. Also, for such events, (personally speaking), greater importance is attached to the opportunity of meeting similar minded entrepreneurs in the same stage or maybe a bit further up the growth curve, rather than the opportunity to meet 'vulture' (er sorry venture) capital firms.
Have you tried meetup.com? Meetup.com helps groups of people with shared interests plan meetings and form offline clubs in local communities. These meetups are free.
There are lots of (mainly free or nominal entry fee) technology-based user groups, meetups and events. Meetup.com 's a great way of hunting down groups.
I'd want to highlight London Open Coffee, which meets Thursday mornings at UCL (near Euston Square) and primarily connects internet entrepreneurs in an informal and unstructured way.
Morpheous - presume you are aware of http://network.businessofsoftware.org/ which has a fairly strong UK bias. Members organise informal dinners from time to time, either in London or Cambridge - I have been to one so far, which was both quite enjoyable and quite useful.
We could always start a UK-based Answers.OnStartups event - I would be happy to help organise - you can find my contact details in my profile. Perhaps other UK-based readers can comment as to whether they would find this useful?
The other route you might find useful from a networking perspective is vendor events. I'm primarily Microsoft technology based and have been to one or two (free) Microsoft events - you sometimes get to meet some quite relevant people. I'm sure other vendors run these sort of things and maybe you can find something that is relevant to your platform/space.
Hope this helps.
If you are in London you may also find the new Google Campus facility useful.
http://www.campuslondon.com/ They have events, opportunities to get access to some interesting people and there is also shared workspace through http://www.techhub.com/ (although not free and some other interesting but not free events they organise too)