The International Centre for Mathematical Sciences (ICMS) in Edinburgh (Scotland) offers Research in Groups. This institute is associated to the University of Edinburgh and Heriot-Watt University.

There’s more information on the linked page, but the gist of it is this:

• 2-4 researchers wishing to organise a short, intensive period of research in Edinburgh
• at least one researcher must be based in the UK
• not all researchers should be from the same university, with a maximum of two researchers from any one university

There are three deadlines for submitting a Research-in-Groups proposal each year: 30 April, 30 August and 30 December.