Flying was never illegal. The CAA put out guidance but did not enact any legislation. However the Coronavirus Regulations - the law - made it illegal to leave your house unless you had a reasonable excuse. So you could fly to work but not for a jolly
The Regulations in England have been amended to allow you to leave home 'to visit a public open space for the purposes of open-air recreation to promote their physical or mental health or emotional wellbeing' and the guidance says this means for leisure activities and the CAA advice on the guidance on the Amendment of the Regulation says a jolly is leisure. No wonder Dominic got confused
The Amendment does not apply in Wales so you cant leave your home. That is the restriction.