The interest rates for Turkish Lira is high, but also is the inflation.
So in your scenario your 40.000 sterling makes about 290.000 TRY. And right now the highest monthly interest rate is %24. So that brings a net interest of 5.000 TRY in 32 days.
Depending on the city & area you live and your lifestyle that amount can be enough.
BUT there are a few important points.
- You have to convert your money to TRY for that interest and exchange rates are usually going up. So if you decide to go back to Sterling you'll most likely lose some money.
- Turkish economy is not stable and interest rates fluctuate a lot. So every month your interest rates might change. For the last year interest rates were fluctuating between %17 and %26.
- Also the biggest risk is about the inflation. If you spend all of your interest and don't add any to your balance because of the high inflation in a couple of years your interest income would afford less. So, I wouldn't advise to spend all of your interest.
- As I mentioned the city & area you live in is also very important. You get the same interest rate everywhere in the country, but the expenses vary a lot.
As from your message about buying a house I think you're planning this for long term, and for long term this scenario has some risks.
I hope this was helpful.