Tell your hosting company that the certificate they've put on your site is self-signed, and not issued by a Trusted Authority.
They'll know exactly what that means, and should fix it up in a couple minutes if they actually did buy a legit certificate for you.
And tell them to visit your HTTPS address: https://www.nairnshire-modelling-supplies.co.uk and see for themselves that the server is clearly not configured properly for SSL on your domain.



