Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you with your poor wee one today.
I am so very sorry to hear the tragedy that has befallen Tiger and your recent loss of Amber. And unfortunately, if Tiger cannot feel his back legs then this is a very serious state for him and his prognosis of recovering is poor if not grave. A lack of sensation in the back legs is often due to spinal damage and is often accompanied by a loss of the ability to empty the bladder (which is critical to life and fatal of they cannot urinate). With some cats we may regain function with time but in the majority we do not and they have to be humanely put to sleep.
Now I appreciate you are a pensioner and funds are limited. Still you can ring your vet and see if they can help you. With Tiger in this serious state, they do have a duty of care to relieve his suffering. If you explain this situation, they may be able to waive a portion of the charge or offer a payment plan to help you. At the end of the day, they don't want poor Tiger to be suffering just as you don't.
If they cannot make an exception, then I would advise contacting the local RSPCA branch (LINK ). The RSPCA does have some hospitals that they will see animals directly (ie London, Salford, Birmingham) and being on your pension does make you eligible to use these facilities. If you are too far from an RSPCA hospital, then some branches can still help cover the cost of euthanizing Tiger. To do this, they may have you take Tiger to their vet or perhaps will pay for him to be put to sleep by your vet.
As well, just to note, if you are on any benefits (ie council, housing, etc), then you may also be eligible to take Tiger to the PDSA. There service is based on donations, so you'd only have to pay what you could. To find the PDSA nearest to you and check your eligibility, you can check HERE. And in case you are local to London or Grimsby and in their catchment area, the Blue Cross (HERE) can help as well.
Overall, this is a terrible situation for you to have to face with poor wee Tiger. I would suggest ringing your vet and explaining the situation. They won't want to let him, suffer and may be able to help you. If they cannot, then the RSPCA would be the next best contact to get Tiger help. And if you are close to the others and qualify for their assistance, they too can be options in this very heart wrenching time.
Please take care,