Rover 75 Connoisseur Overheating

i am the owner of a 04 plate rover 75 connoisseur that keeps overheating have checked the head gasket and is fine also have checked pipes and system for blockages all to no avail any advice on what else i could try would be helpful . thank you

Honestly not trying to undermine you here but how did you check the head gasket?

It's not uncommon even on a 04!

my rover has been overheating fo a while and ive tryed changing thermostat had heads checked and mechanic said it was radiator but im sceptic about this any advise would be welcome oh its a v6