Stored Contacts Numbers not recognised

Why have all my saved phone numbers with a stored country code format (ie +44 (0)20 8nnn nnnn) stopped working when call is initiated from Contacts on my iPhone11. Every one comes back as "number not recognised". I believe these numbers have stopped working since the last s/w update to 15.2.1

If I edit the number to just the std code & number, the call goes through.

Is there a workaround as I have a number of international numbers stored