The only benefit you need to be on is Housing/council tax benefit.
Even if it is only £1 benefit, it ensures that you can get your pet treated at the PDSA.
I know this because my dogs are treated at the PDSA so I know the procedure.
You can also get flea and worming treatment from them at very good prices. Frontline is much cheaper at PDSA
You can have the dog microchipped for £12.

If you don't recieve housing or council tax benefit tou could always ask the RSPCA for help with costs of any expensive treatment.

Good luck with your new dog, I hope you have many happy years together

I do hope you get to keep the dog,if they are any kind of animal lover they shouldn't charge you.They should be grateful the little one is going to a good home.God bless you both.