Out of interest, what could a radio service (such as Stapleford) be able to offer?
Please correct me if I am wrong - but I am pretty sure that Stapleford only has Air-Ground. The only service they are able to provide is an "Air-Ground Communication Service". This means that they are able to talk to you from a ground based radio, pass airfield information, tell you about any traffic that is known to them, along with any other information they feel appropriate for your flight. It is important however, that Air-Ground operators are not generally allowed to "clear" anyone to do "anything", although they may tell you to do something, it is at the pilot's discretion to follow any instructions given by an air-ground operator. (although generally, they have a pretty good idea what's going on, are pilots themselves, and actually do a very good job at helping you)
What has worked for me so far is "assume he's below the clouds and that I'm the only one daft enough to fly in the cloud on purpose".
You just have to pray that they're not stupid enough to actually be in IMC without a working mode C (or 3A) transponder and deliberately not talking to any ATSU. I think if that was the case, I would request a deconfliction service assuming that the "no height information" is the same height as you.
It is/was normal for Blackbushe based instructors working Farnborough West to ask for RIS/Traffic Service when doing upper airwork and climbing or descending through cloud, reverting to FIS/Basic when clear of cloud.
That is what I hear frequently on the radio at Biggin, so I assume that this is common practice.