Ok so my phone has gone into a bootloop, and nothing it seems will cure it. I have tried a factory reset, firmware upgrade and installation in Kies but no joy.

My original S3 was in a contract with T-Mobile, but that got wet so was replaced by Halifax insurance (Lifestyle) in April. My question is, who do I go to? I no longer have the insurance with them as I changed banks to Nationwide. Some people say ODIN would fix it but I worry that it may void the warranty. Anyone got experience of this?

depends on the dates. If it's under warranty (generally 2 years for Samsung I think) , get it fixed under warranty; contact either the retailer or Samsung directly.

If its not, then whether or not ODIN invalidates warranty is irrelevant.

Lifestyle unfortunately are largely shit, so you're best off rid of them at least.

Just remember if it was because you bricked it during rooting it may not be covered.

Mine did exactly that after a Samsung ota update, Samsung told me to take it to my nearest repair shop which was half hours drive away. On collection next day they told me nothing they could do as it had been rooted and charged me £15, I've never rooted any of my phones, i wouldn't know how to.
Ended up speaking to Phones4u where i originally bought it from, they sent it away took about 1 week and got it back all fixed.
Mine is now away again!! through P4U thanks to Samsung's 4.3 update screwing it up yet again, and again Samsung have done nothing to help people out affected by their cock up.

I know it silly, but have you tried removing the micro sd card? Mine was stuck in a boot loop and after hours of trying to fix it o tried taking the memory card out and worked perfect since.

Thanks for the replies. Its within warranty, and its never been routed. Running standard 4.1.2

I have tried it without the SD card, still no joy unfortunately. I rang Samsung and they told me to take it to my nearest service centre, about 20mins drive so could be worse. Samsung say if they can't fix it it's gotta come back to them. My only worry is I can't find a receipt, the original was with a T-Mobile contract and then the new replacement with the insurance. If it has to go back then its 2-3 weeks Hoping for a new phone actually as the glass it scratched but see what happens...

Reading on the web the bootloop is quite common. I have had it once before but a factory reset cured it last time...

Seems it was a German S3, how odd....anyway they could not fix it either so it's gone off to Samsung....1-2 weeks to wait...