Hardy Tropicals UK

In this heatwave I'm not sure how much water per watering can and how often a week would you water both potted Trachycarpus and Trachycarpus in the ground,please help.

Potted ones should never be left to dry out. Those in the ground will do better but still need a good soak. A weekly feed and soaking when dry to the finger is a good approach.

I've had a Trachycarpus in at the back of our house for around fifteen years. Once it settled in I never watered it and I only started feeding ti last year. Its in a very sunny location, full sun, no shade in a windy location. It gets a lot of reflected heat of the back of then house and its in well drained soil. It was a tiddler when planted but its now reaching the first floor.

it would also depend on when planted .Newly planted ones(this year)will need more watering than an established one.
As for potted ones depends on location some may need watering twice a day if in sunny area.How big is the watering can
I assume at least 7 litres.