thanks. I've been doing seem reading and it certainly sounds like it could have been that.

I had a very similar incident in January this year too as we were descending an alpine pass. Same problem with power but since we were on such a steep and long decline I managed to keep the car running and by the time we got to the bottom it seemed to sort itself out enough to fill up and has been fine since then till last week. That was also at about 1/4 tank level but with the car on a steep decline.

I have regularly run to below 1/4 tank since then too.

Will fill it up and keep it topped up and see how things go. If that seems to cure it will just fix/replace the siphon pump I guess.