Two issues have got confused here.
I didn't call Marham for LARS because I was transitting above Lakenheath, not Marham. I wanted (a) DAAIS for D208; (b) FIS from Lakenheath, and failing that at least a listening watch on Lakenheath, so I was aware of traffic. A RIS from Marham would have given me so many conflicts, especially as I had no Mode C, that it would not have made life any easier.
The bit about LARS was a reply to a comment that LARS units are often too busy to provide a radar service - and I don't like flying in IMC without, so am a bit concerned if that is often the case. I find Brize generally brilliant, but for longer trips I obviously need to use other LARS units...
Tim