Mary I am not sure that Benson would have been able to provide a radar service especially on a Sunday - Brize and Farnborough would but I am not sure down to what level.
We don't have pre- canned low level IFR routes in here so far as I know except for departure from major airports -eg. the "Juliet" departure from Luton and possibly heli routes within the London CTR/CTA.
Some speculation on other forums about non-published IFR let downs into Chalgrove- these could be GPS based, or based on the WCO NDB or the CPT VOR/DME if you knew how to use them.