Hi there,
at the company I work for doing passenger trains out of London, we have a number of drivers from EU countries, examples being Poland, Netherlands and Spain to name just a few.
Please bear in mind that this career is in great demand in the UK so not at all easy to get into. You will need to demonstrate that you have worked in an environment where safety is vital, perhaps have some customer facing skills and to show high levels of concentration. If you do not have this experience then due to the amount of applicants for each train driving job then you are unlikely to be offered a place on a training course. If this is the case then a good route in would be to get a job as a bus driver first as I know that quite a few of my colleagues came from a bus driving career into the railways.
Without wanting to put you off, the training is quite intense and you must have a good grasp of the English language, firstly so that you absolutely understand what you are taught in the classroom and also because clear and understandable verbal communications are required on a daily basis, an example being when you need to communicate with the signaller. Doing something wrong because you did not understand what the signaller told you or he did not understand you, can have major impacts on safety and possibly lead to loss of your job.
Good luck with your quest, I am sure other posters on this forum will be along to add to what I have put.
EDIT: to further answer your question, there is a 'sticky' post at the top of this forum page detailing the steps to becoming a train driver.