thanks for the awesome advice. Here's where I am at the moment...

1) went to a pilates one-on-one session & got a series of basic hip/core strength moves.
2) started glute exercises - kneeling squat, back bridge, clam
3) a specific stretch where I stand one foot on a table, leaving the stretched leg being stood on. This was a real stretch to begin with, right down inside of thigh, but it's become easier.
4) hip flexor stretch. creates very tight feeling down front of thigh

they have helped a great deal. I now have greater flexibility in the hips, especially the troublesome right one. No great pain when walking as everything seems looser.

BUT...even a short session on the bike flares up the inner thigh (right about where the gracilis is) and the attachment spots of the medial knee tendons. No screaming pain, they just get very hot & bothered. I take cold baths post cycling but that doesn't really solve it. It's still keeping me off the bike as even a 20 min session leves me with very tight hamstrings & inner thigh afterwards. I can feel them tugging at the inside of the knee until thye're rolled out.

I saw the physio again who commented 1) that the legs were looser but that 2) there wasn't a great deal else they could do. I still have sports massages booked.