plastic pipe stuck inside copper nut & pipe

[Popzdad]

Thanks, had it double checked by a pro and should all be good now

 

[Gasinspect]

dig out the plastic with Stanley knife, bradawl, fine nail, pointed kitchen knife. then clean thread with a brass 1/2 male fitting screwed in and out a few times; get a brass shanks fill valve (screwfix do one) to avoid risk of shearing plastic stem in future.

 

[Ric2013]

dig out the plastic with Stanley knife, bradawl, fine nail, pointed kitchen knife. then clean thread with a brass 1/2 male fitting screwed in and out a few times; get a brass shanks fill valve (screwfix do one) to avoid risk of shearing plastic stem in future.

The OP's already done the job now, I think.