Tässä vastaus ruotsalaiselta kaverilta, jolla on 1100 Sport ja kunnioitettavasti tietotaitoa:
First, the ECU can not actually make the diagnose "petrol pump cutout" with any certainity, as it
a) does not get any feedback on actual fuel pressure, and
b) does not get any feedback on [electrical] pump current.
It could theoretically sense that the current passing the power relay coil is too small, but that would be it. If that's the case, the correct error description should be power relay coil cutout, although the fuel pump (as well as the injectors and spark coils) will obviously lose power as a result. I have no idea what the code really means. It could even be just "deceleration when expecting acceleration" and in that case this error would also pop up if you run out of fuel or even outpower the engine with your rear brake.
I would check the power relay and the ECU relay (and why not all relays) as well as the ground strap fitted to the ECU cover. Relays are said to be failure prone but I think the sockets are even worse. Clean them and grease with battery pole vaseline, and perhaps even use zip ties around the relays (I've had the power relay pop out of its socket twice in 150 kms!). In case a relay is actually bad, swapping them around should make the problem move or go away.
When this appears, does turning off headlight make any difference?
Ignoring the codes (sometimes they are just there to confuse you) I would replace the fuel filter.