Leisure Tank Gas Leak

[maxstu]

Not from bolt but coming from behind this plastic stopper.
What is behind it?

Regards
Stuart

[maxstu]

Answering my own question, after more internet browsing, apparently this is a pressure relief valve and is working as it should.
Recently l filled up with LPG five miles away from home. This is to stop excess pressure in the leisure tank if ambient air temps increases and expands the gas.
Will monitor tank gauge.