There are flights from cities in the North of England (Manchester, Newcastle) and Scotland (Edinburgh, Glasgow and Aberdeen) into LHR. However, as Aviatrix says passengers in these areas have the option of connecting at other European hubs such as AMS and FRA. LHR is a very congested airport with limited slots and long-haul routes are far more lucrative than domestic services.

You mention that you are in the West of England, I presume that if going by public transport, you take the First Great Western train service to Reading and catch the Rair-Air link bus to LHR?

I think for people who live in UK the issue is not the lack of air links into LHR from regional airports but the fact that LHR is not part of the national Intercity / Crosscountry rail network which means that if you want to travel from one of the major cities to LHR by train you usually have to travel into one of the mainline London stations, take a taxi or the Tube to Paddington, and then catch the Heathrow Express to LHR (or take the Tube all the way to LHR).