I’ve created a Google Calendar of London events of interest to software developers and web professionals. If you search for a public calendar called “London Geek Events” you should be able to add it, though it can take a few days for new calendars to appear in such searches. In the meantime, click “manage calendars” and “add calendar”, and use the iCal or XML urls for the calendar.
I’ll need some help maintaining it – if you’d like write access to it, or simply want an event adding, let me know.