At the risk of pointing out the obvious : Why don't you ask the cafe owner whether it's Ok if you hang out for most of the day at a table - and whether they'd p

At the risk of pointing out the obvious : Why don't you ask the cafe owner whether it's Ok if you hang out for most of the day at a table - and whether they'd prefer you to pay via regular coffee purchases, or they would be comfortable if you just gave them (say) GBP10 for the morning, etc. Make sure the place has the right vibe before you pick it for the 'long term', and that you make plain that you're happy to play by their rules...