VW Polo Tail light issues

I've been having an issue with my right tail light, it only happens when we don't use the car for a couple of days.

When I first switch the engine on the warning light comes on the dash indicating that there is a problem with the lights, when I switch the lights on the right tail light doesn't work, all other lights appear to be working. However, after approx 5 minutes (or less) of driving the tail light comes on. The warning light on the dash remains on until you restart the car, when it disappears.

If I immediately try and restart the car after noticing the problem the tail light still doesn't work and the warning light stays on, then after a few more minutes the tail light comes on and the warning light stays on until you restart.

If I have used the car recently then both tail lights work and the warning light doesn't display.

It's a bit confusing but I hope i've explained it clearly! Does anybody have any idea what it could be or have experience something similar themselves? The car is still under warranty but the garage said they can't tell me whether this fault may be covered or not until after an investigation, which if it turns out not to be covered will cost me £70 :( !!

Thanks for any help!