This is a dog's breakfast due to chronic underfunding of air traffic control in the UK, this means we don't get the level of Flight Information Service that is common elsewhere in Europe.
In increasing order of service:
To get a basic service all you need is a radio. Basic Service in practical terms means you are known to ATU and they will answer questions for yuo like "What's the QNH at AAA" What's the weather at AAA" "Could you activate my flight plan please?" If you don't want any other service and know the answers already I wouldn't bother to talk to them.
To get a traffic service a transponder helps the controller, but you only really need a radio. The controller needs a radar set. Traffic Service means the controller will try to notify you of potentially conflicting traffic and other hazards like controlled airspace and danger areas you might infringe, but if he misses one or forgets that's still your problem not his. However it's the most useful service as you get an extra pair of eyes and all the stuff that goes with basic service.
Deconfliction service is like traffic service except the controller will give you a heading to steer to get round it, since that may take you into IMC it's really only for IFR traffic.
Procedural Service is mostly so that IFR arrivals and departures at airfields without radar can be safely sequenced.
Hope that helps