Can it be done, and if so could someone tell me how please 

No, it can't.

Cheers that’s a pain!

New tank is cheap and easy to fit. You don't even need to drain the coolant. Just top up the small amount you lose when changing the tank.

Bit of a thread hijack, but will low coolant (below minimum mark) trigger the engine management light (the yellow engine outline one). 

No.

No. That tends to be for things that will have an impact on tailpipe emissions. Low coolant has its own warning light.

Thanks for that, it has answered one question and posed another as it were.