All UK cover should include 3rd party within the EU for the duration on the policy. LV (Liverpool Victoria) does comprehensive cover for 180 days as optional extra. There are a couple of others that also do this length although can’t remember who.
I’m surprised if there is a particular exclusion written into policies for you flying back to the UK. If this is the case, then I am guessing that it would only apply to the comprehensive part, and that you should still be covered for 3rd party. If you have paid to park while you return to the UK then the car park owner MAY have a liability for any damage to your car while you are away. In the UK they would unless there is a specific clause that you are made aware of before you make the contract for parking. Can you elaborate on how you have been made aware that you are not covered while returning to the UK, and how the contract term reads please?