Ice Pack -
If you have no clearance, you do not join CAS - flight plan in the system or not.
If this happens again, why not contact Brize on one of the other boxes and tell them your predicament - ask the Twr Sup to speak to London if it is so bad.
Gotta be better than effectively blundering into CAS. The fact you were in a 200T A/C matters nought..... one of many in the airspace you wish to join, most with fare paying soft civvy passengers who would be most disgruntled at having the G and Ts spilleds as the crew complied with avoiding action to miss you!!
P.S. - if all the controller said was 'thank you' then
a. turning 5 miles before airways would be correct course of action, and
b. The controller would not have cared as it seems they did not even offer you a FIS, never mind RIS or RAS!