This varies with the hospital you work at, but you would typically be paid about £1500-£1700 per week worked, before tax and National Insurance (NI).
After tax and NI you would be left with something between £1100-£1200 per week worked. Assuming you work a two weeks on - one week off rota, you would work three weeks per calendar month, so you will earn an after tax average of about £3300-£3600 per calendar month in which you work three weeks. This would be the equivalent of 4000-4500 Euro. Notably, you can calculate that your hourly rate is about £7, which is actually very low for a physician. So you are not well payed, you earn a lot because you amount a lot of hours. Also, rest assured: you definitely won't actually work for 24 hours a day.
Typically, you would have one week off with holiday pay, about £130.
Also, during your stand-by week you'll earn about £750 if you are not actually working, normal pay if you do.
Some companies offer a significant bonus (over £1000) upon successful completion of a six month contract.
In conclusion, RMO work is well worth money-wise for doctors coming from poorer countries.