Not credit card, definitely. If you can get a mortgage extension do that, it's usually the lowest interest rate available and the terms will be longer. Banks are usually happy to lend on that basis if it adds value to the house.
We have already saved up quite a lot more than that amount and I really am getting depressed with the state of our tatty house. We have lived here 7 years and I am 50 next year and really can't stand the thought of living in semi-squalor much. This £5,000 is the last little bit needed for new carpets, some replastering and stuff. We have already saved enough for a new kitchen. I have a long and sad posting history about the state of my house .
Cheapest borrowing will be extending the mortgage and then paying a lump sum off next year. If you don't want to do that a Personal Loan would be a good option, but you'll be looking a much higher representative rate.
If you can pay the full amount inside a year & you can pay for the work to be done with a credit card (do plasterers take plastic?) I'd probably go for one of the 0% cards and be very sure to pay off the balance before the 0% expired.
Credit card could be expensive, unless you can get a good deal and pay it off in a year. Mortgage extention - depends on what kind of mortgage you have, any arrangement fees, penalties for early repayment etc. Loans - shop around and see what you get, I got a reasonable deal with a loan from my usual bank but that's not always the case.
We are going to get a 0% credit card - I'm amazed at how many are still available, for up to 18 months, in this supposedly credit crunched day and age. That and an interest free kitchen from Ikea means we can definitely start in a month or so - v excited.
Have you considered your local community or employer-run credit union. Rates are good, and you can pay it off in a lump sum if money becomes available with no penalty for overpayment. I use this to buy cars and fund large household projects. Your local council may know of where your local one is.