Have checked the air shut of valve and it seems to be fine.

Doing so, I did notice the hose which leads to the manifold has a big split in it. Maybe this is the cause, will pick up a new one from the scrappy Saturday as it's a dealer only part and they want £64+ VAT. For a hose!!

The battery is a year or so old and is fine, even when jump leads connected to another car there is no difference.