Lastminute.com checked baggage

looking at flights and included with economy is only an 8kg carry on bag, lastminute says you can add checked baggage in your account section on the website but that requires you to first book the flight before you see the price. how much do they charge for one checked bag each way upto 23kg/50lbs? flights will be with British airways
anyone had experience adding checked baggage to their booked flights? thanks for any advice