NickB

That is not the case. First, there are no restrictions on travel in England which does not involve an overnight stay. What there is is (non-binding) guidance. Second, the guidance does not restrict public transport to essential journeys only. With respect to public transport, the guidance is to try to minimise access to public transport as much as possible by considering alternative forms of transport first and, if taking public transport, preferably traveling at off-peak times.

More broadly, and beyond public transport, the guidance advises to minimise travel as much as possible and to ask oneself whether the journey one plans to make is really necessary. It is plain that a leisure trip of the kind envisaged by the OP is without doubt contrary to the guidance regardless of the use of public transport. However, it is not prohibited by any binding rule.