RR.
The need to call Manchester is one of those procedures that have applied since Bleriot flew the channel. It would be a possibility that Liverpool could work the LLR. The only problem would be, would they want too? Liverpool would be in the same situation that Manchester are, in that the money men who pay for the ATC service would no doubt say. "What do we gain from providing this service", and the answer, a service to the GA community transiting the LLR, wouldn't convince them it was worth spending the money on ATCO provision. Now, don't get me wrong. I'm not saying I agree with this approach. Unfortunately it's a fact of life these days. Personally I like the idea of a dedicated frequency for the LLR where aircraft can perhaps use a dedicated conspicuity SSR code and announce their position with no ATC involvment. I believe this is the basis of Whirlybird's post above regarding Los Angeles. Then there is the thorny point, do you make it compulsory for aircraft to make position reports. Otherwise you'll still meet unknown traffic? I'd be interested to know if anyone else thinks this is a good idea.
Spiney.