Are there any laws about raising other countries flags in the UK?
No. Nothing stoping you.(although you need permission from the local council)
My understanding of the law. is that you can put up national, state, or regional flags, or flags of authority, but nothing that would constitute advertising or anything offensive.
The advertising one is also why the council will make you remove something like a football flag etc if you put one up. Although the rules regarding flagpoles are different and specific, than say, putting a flag in your window etc. which comes under different legislation.
• Under the Town and Country Planning Act 1990, flags come within the definition of "advertisement". Their display is controlled by the Town and Country Planning (Control of Advertisements) Regulations 1992.
• However, under Schedule 2 of the Regulations, the national flag of any country, and this includes the Union flag, is exempt from advertisement control provided each flag is flown from a single vertical flagpole and neither the flag nor the flagpole display any advertisement additional to the design of the flag.
It is recommended that any proposal to erect a flagpole should be submitted to the Planning Department at the Local Authority to ascertain any local regulations.