Not exactly the easiest situation to judge. Whilst in an ideal world, the entire force would be at full force all of the time, I don't think banning muslims and/or ramadan from the police force would be particularly productive. Dividing society is hardly going to help muslim relations in the UK.
Surely the logical answer is that, at the very least, officers taking part in ramadan should not be put in front-line situations where peak physical fitness and mental agility is required. However, at the same time, it seems unfair to pay them presumably increased rates of pay over other officers, if they're just going to sit in the station filling in forms all day - they aren't earning their extra pay. Then though, we're in a situation where people are effectively being paid different rates according to their religion, and doubtlessly many officers would deny they were incapacitated and remain adamant that they could continue their job (and receive the extra pay).
So as far as I can work out, the only logical solution is to take them off front-line duty for a brief period, and if necessary extend the same offer to non-muslim officers for the same period each year.
It would probably cost a fair few bob, but it seems a better option than just denying muslim officers the opportunity to practice their religion.
At least to me it does