But that's a different argument. Boris is saying Heathrow R3 is a greater environmental disaster than Boris Island.

That is likely to be very very wrong. He's either lying or ignorant.

Your argument might have validity, but on this Boris says no R3 because it would be an " environmental disaster". If you want to defend him - as you appear to be trying to do - you need to explain why R3 would be a greater environmental disaster than destroying one of the most important wetland areas in the UK. And since I know you don't have the professional experience in this field, just saying so won't convince me.