What a decent employer should do is undertake an individual consultation process with employees when they will explain the proposals and ask for individual reactions. At such a meeting you should have a full opportunity to explain the difficulties you would have, which will clearly be far more substantial than for someone who drives to work. Its reasonable for them to try and come up with something that is reasonably for you, and from what you say, they would like you to come with them. For example, they might be willing to fund the cost of a taxi for a period of time - an 8 mile each way taxi contract would not cost the earth compared to filling your vacancy - depends on what you do, of course. But don't expect them to do that for ever - perhaps 6 months. The 'problem' has to be owned by the employee, but the employer should try and take steps to help solve it. If you really can't make the move long term, they should help you to find another job - time off for interviews perhaps. Company moved don't occur overnight and I'm sure you are getting 6 months or more notice of this. You might wish to ask if redundancy is an option they would consider, but they may say no.
I think you'd be pushing it to demonstrate unfair dismissal if they had done the steps I outlined above. They would probably seek to dismiss you under the 'Some Other Substantive Reason" clause, which is regarded as a legally fair reason.