Here is a list of the major European retro rides:http://www.retroronde.be/nl/190-kameraden
There is nothing in the UK on that list, so the closest are probably the Belgian ones (Retro Ronde van Vlaanderen etc).
The Eroica is still the original and the best, it's 200km so it's quite an athletic challenge. Most other retro rides are only 100km or so for the longest versions.
The Retro Ronde is still very atmospheric and you get to do some of the famous Flemish hills.
There is talk of a British version of l'Eroica, but I've no idea how serious this idea really is, and if it will come to anything.
Personally, I'm dubious about it, I think it would be better to build a retro event around historic British cycling and terrain (Shibden Wall? Mow Cop? Box Hill? A ride around London ending in Herne Hill?) rather than make some fake copy of an Italian event. Mutter, grumble...