I’ve got avon rangemaster tyres on the Landy I got earlier this year. I’m not getting on with them at all. Road grip seems to be poor and they are no better offroad. Anyone else had experience of these tyres?

they have plenty of tread on them so i was hoping not to need to change them....

Dunno. Try lower pressures?
Try the manufacturer's site as it will give recommendations for approved fitments. These will often differ from the oe pressures.