You can probably get it via the NHS but there'll be a massive waiting list. You may find that a cardiologist won't do a standalone exercise egg without a normal one plus cardiology report (extra, obvs). For the whole thing (normal ecg, ultrasound, exercise ecg, 24 hr ecg) was about £500 a couple of years ago, maybe half that was the exercise ecg from my local private hospital. If you're employed your company might cover that, my private (via company) health insurance paid up. I guess any decent private hospital would do this - maybe start with a search on the well known provider site?
Good luck, hth