Is it my pedalling method or something about the pedals/cleats that causes me to often unclip on the upstroke?
Happens at any time – pulling/pushing hard on steep hills or just on the flat. Seems to be towards the top of the stroke and it seems the back of the cleat comes out of the clip. The tension is high so its not that.
Anyone else have problems with this? Have had experience of this from near the start of my spd use but has got worse as time has gone by – could be cleat wear but that doesn’t explain the early happenings.

I’d have put that down to either a worn cleat, or a cleat mounted at a funny angle. If the cleat is straight when it’s engaged you might be twisting out as you pull up, it only takes a degree or two of mis alignment for this to happen. So maybe try looking at the angle of your cleat relative to the angle your feet sit at naturally?

If you’ve got ten to two feet and you haven’t set the angle of the dangle it could happen, sit on something that lets your feet hand free and set the cleat so it’s straight while your foots at its normal angle.
If the cleats straight on the shoe it might be close to the release angle while you’re pedaling..

I had a similar problem when I fitted multi release cleats by mistake. They are designed to release upwards as well as sideways.

Maybe you purchased some of these

I wrote some reasonably sizeable instructions for someone else the other day on how to get setup, could be worth a read.

Interesting points about the angle of the cleat. Will check that out. Although yesterday there was something about my setup that made it nearly impossible to unclip for a while, had to put all my weight through the pedal and twist to get out – just twisting the foot was not enough, yet 20 metres down the road on the flat it just popped out at the top of the stroke.

Although yesterday there was something about my setup that made it nearly impossible to unclip for a while

Check for any sharp barbs on the peddles and cleats, if there are any just file them off. I had this after hitting a peddle on a rock reasonably hard. As soon as a filed the little barb the rock damage left they were fine again.

They aren’t multi-release, they are the standard cleats.