If you're set on Mef jobs in London, there aren't very many at present: we count 5. Why not check out nearby locations on Jobspotting? The job opportunities can be broken down into the main categories .NET Framework and Microsoft APIs. Swot up on Wcf, Mvvm and NHibernate to make sure you're the right fit for vacant positions like this.
At this time, employers are exclusively looking for very experienced candidates. None of the employers currently advertising Mef jobs are startups. Recruitment companies are used by the majority of employers searching for talented people. If such jobs aren't the most appealing for you, feel free to filter your Jobfeed. Why not have a look at vacant positions in another country to compare and contrast opportunities. Just use the Explore tab.