Hi Simon,
We actually use two Linux servers (albeit hosted by the same company) and I can reach neither via SSH on port 22. They are two separate machines with different IPs so that's why I was suspecting NTL as stopping this traffic.
My colleague who works on the server at a different site can connect fine so the port is not blocked server-side. Linux is not my strongest point but I don't believe there are any ip-specific blockages either. Also suspect is the fact that I could connect OK over a two-day period (without any adjustments to the server or PC) but then reverted back to its old behaviour.
I may try a dial-up connection to see if I can access the server this way. Back to the old school, eh?