I frontlined my dog a week ago today, a few days later he developed a swelling where I had applied the frontline, anyone else had this reaction and what can I do to reduce the swelling?

That's quite a long time after the application, but I'd certainly mention it to your vet as a possible reaction, and use a different treatment next time.

Yes, I thought it would have gone down by now but it hasnt, its like a lump.  The skin is not red or sore looking, its just a swelling/lump (about 6cm wide)

I'd let the vet have a look at it and report the reaction to the manufacturer. Then if any treatment is necessary for it the company will probably pay for it. I've only seen this once before, and that's what happened.

My dog had a bad allergic reaction to Frontline (not the same reaction as no swelling but immediate shock, panting, salivating etc) but I do wonder if the vet reported it to the manufacturer. Previously we had been told it was perfectly safe and reactions are unheard of.

Yes it is most likely to be the frontline, dogs can and do get adverse reactions to flea treatments, wormers and boosters.  Frontline is very strong and some dogs have actually had their skin burnt in the area it is applied.  A dog I had used to go very strange, rolling over and then used to look at the wall in a daze for a couple of hours after using flea treatments.  Unfortunatley I used to believe the vet when he said it was unlikely to be the flea treatment, and I continued to administer it every 3 months.  Complete fool!

You can protect your dog against fleas by feeding them garlic each day fresh or capsules and also by adding vit b (like brewers yeast) to their diet.  It is effective and safe.

It might be worth giving your dog some Thuja (homeopathic remedy) for a few days which will help with adverse reactions.