two follow ups to this:
1. pour the lager in after the cider, or it will froth everywhere.
2. The ribena mixture makes what is known as a Purple Nasty.
3. They are much better coldish.
4. To the above recipe, add 1 shot of Blue Cucaro to concoct a Green Monster. (note! drink very few of these, the combination of 40 proof alchohol plus the mixture of hard cider and lager will knock you right on your ass.
see also real drinkers prefer their drinks to not be bright blue.