What do you mean by "modern" redzed? Right now, or some specific post-WW2 period? The soldiers you can see in "Our War" in Afghanistan on BBC3 at the moment look quite different from their predecessors who first went there 10 years ago - new helmets, new body armour, new camo ...
Osprey hasn't really kept up. There's a Mike Chappell book on "the British Army in the 1980s" (Elite 14) which would be handy for the Falklands or the BAOR in an imaginary WW3, and a volume on the British army 1965-1980 (MAA 71) with Angus McBride plates, both of which I've got and seem quite solid.
The Royal Marines get three volumes: an MAA (1956-84), an Elite (1939-93) and a Warrior (1950-1982). There are some MAAs covering specific conflicts in Malaya 1948-60, Indonesia 1962-66, Northern Ireland 1969-92, and an MAA just about the British forces in the Falklands.
Brits get some mention in two volumes on Special Forces in Iraq and Afghanistan and in "Armies of the Gulf War", and there's a Mike Chappell MAA on infantry equipment 1908-2000 that inevitably shows some uniform details too.
For anything more recent, cheap printing means that there have been lots of books of photojournalism about the wars of the 21st century: they'll give you lots of pictures of recent uniforms, but are unlikely to explain or contextualise them.