04 Peugeot 307 1.4 petrol 16v - Peugeot 307 1.4 petrol head gasket replacement - jag...

my 04 Peugeot 307 1.4 petrol 16v has done 42000 miles. In its recent service the peugeot dealer flagged up an issue with the head gasket and said it needed replacing. the car is not smoking, not losing oil or water, not overheating and there are no visual leaks on the engine block.
how urgent is this job and does it warrant the £1200 price tag the peugeot garage put on it?

Many thanks jag...