Shoreham probably has a lot more IFR traffic than say Thruxton or Old Sarum but unless I really need to leave at a certain time I'm not too bothered about the possibility of having to alter my timings by an hour or two to get an IFR slot. By all means try and get around the system but would it really be worth the trouble compared to just adjusting one's plans accordingly? Unless of course all the slots are taken...
This whole "co-ordination" thing for these small airfields is such tosh though; I mean yes the London area probably needs rationing but for people going South from the coast towards Europe at light aircraft altitudes FL80-140 etc I really don't see how we are bothering London control too much.
I'd curious to see if all this talk of lots of private jet traffic at Biggin Hill etc actually materialises...