@Monika566 Firstly you need to red your rental agreement. If it specifically says you can't sublet then you need an additional agreement. If it is silent then you may be OK to go with a verbal agreement from your landlord but I would send him an email saying ' thank you for allowing me to Airbnb the property....'
Yes you will pay tax. If you are sharing the space then under the rent a room scheme the first 7000 of income is tax free. Generally rental revenues are treated as income so once you have exhausted your tax free allowance you will be taxed as normal.