HMRC publish benchmark scale rates for accommodation and subsistence payments made to you by your employer where you travel overseas, so that up to those rates there is no income tax charge on you nor any exposure to national insurance contributions.
The rates are reviewed once a year and new rates have just been announced. They represent a useful increase which hopefully your employer will implement. They vary considerably between countries and indeed between different areas of a country. Furthermore, the benchmark scale rates are split between items such as room rate; meals (separate rates apply to each meal); drinks; specified travel.