WordPress on a BT hosting account – not working well

We have agreed to run an WordPress account for a client, who have a BT hosting account. They have upgraded to a BT ADvanced hosting package so we could set up databases etc. We have implemented WordPress but it is not working. For example the pages stay blank – see https://www.the-harbour.co.uk/home or take ages to load (if they load at all).

Could this be to do with the BT hosting package? Or is it something else?
Any help you can give would be massively appreciated.

Cheers