As of yesterday the seat does not go forwards when you plug in the key and start the car. All controls work, and it still moves the seat back when you turn off the car. Is it likely to be something simple?
it is a late 96/early 97 Q45

According to the WD for the US/Canada model, the Seat Controller and Mirror Controller are both CAN-enabled, and it looks like the auto-position "memory" is stored in the BCM and occurs on the BCM's request. So if the seat and mirror switches work normally but the auto-position doesn't, it means there's a communication problem between the BCM and one or both controllers. See if the mirrors still respond to auto, if they do then the problem is in the Seat Controller or its wiring. If both don't respond then there may be a global issue with CAN from the BCM.

Hmm, well the seat retracts properly like it did before, it is just the moving forward at power on that is missing. the mirrors fold on lock and they both unfold on power on, I am guessing it is a sensor somwhere in the seat?

No, if the slide position sensor was faulty it would affect operation in both directions. Whatever this is, it's more subtle than that. The controller does have a patch into the driver's door switch, which looks to be a separate throw from the one the BCM uses for the dome lights. Check voltage at the YEL/ORG wire on the door switch and see if it transitions from 0V with the switch released to 5V or 12V with the switch pressed. If it's flat at 0V then you may have a broken wire or bad pin-fit between the door switch and the controller, check the GRN/BLK at the controller (there should only be one GRN/BLK according to the WD, and it's the same wire as YEL/ORG with a color change). On the other hand, if YEL/ORG is flat at 5V or 12V, you have a bad switch or a bad switch ground wire.

Blown away as usual by VStar's diagnosis. Before going too deep, I'd try disconnecting the battery for a while or overnight. Sometimes something simple can reset a glitch when it comes to the memory seat stuff.

wow, thanks a lot. I need to get the voltmeter out.

A new development is that it occasionally works when I put the key in the ignition, it has gone forward a few times now.

The car now has about 55,000 miles on it, I have added about 15K miles in the last two years, but it is a 17 year old wiring harness I guess.