Slight petrol leak out of breather hose?

[ATK 140 1 Cars]

Been a while since I had an issue, odd one today- 

 

what could cause a little amount of petrol to come out of the smaller diameter breather hose running from the cap area to behind the rear wheel arch? Noticed a little amount of petrol coming from it earlier today. Full tank very hot day if that makes any difference.

[Leslie green 109]

Y'm guessing its to cope with expansion and too much fuel in  , it has to go somewhere as it warms up  or the tank would split . If its only a small amount its doing its job