Thanks for the replies. You're probably right, I'm due a service anyway and the front pads came from the mfg contaminated so they're noisey.

But interestingly, after standing upright all day at work it was back to normal for the commute home. Maybe there must be some air in the reservoir which made it's way in to the lines while upside down in the cold. I did squeeze the brakes to ensure the calipers were aligned when I put the wheels back on (still upside down).

At least now I have the option to procrastinate although I take your point I'm probably due a service.