Hey Andy,
Nothing to worry about
If it flashes for 30 seconds then the glow plugs are starting to get a bit old and worn. If it flashes for 60 seconds then they are really worn out.
They are a pain in the ass to change as them get hot and mould into the engine bay so I would get a garage to change them... it is known to snap them and then it's a bugger to sort it but a garage will have all the tools to do it.
The glow plugs are only used in cold weather to help make the diesel turn to liquid (in cold weather diesel turns jelly-like). My light was flashing for a year before I got them changed but I did have a couple of probs starting in winter this year when we had all that snow, I got mine changed that week and it started fine after that.
Obviously it could be another problem but I am 99% sure it would just be the plugs wearing out.
If the car starts fine I wouldn't worry
Darren