Nigel
There is often a transition between going IMC and getting a radar service. In some parts of the country you won't get a radar service in IMC at weekends. Don't sweat it. Providing the handling pilot is qualified then the risk is reduced. Providing he flies according to certain rules the risk is reduced further. Sometimes getting a radar service is just the iciing on the cake.
As has been pointed out - less people fly IMC than VMC, so less chance of a collision, especially if you follow the rules.
CM