Yes there are regs in the UK at least, cant rememebr off the top of me head but 750m and 1500m ring a bell.
A lot depends on what conditions parralel approaches are gonna be made in-LHR for example, parralel approaches have to be done in decent wx so that viz separation can be used-pressumeably if one is gonna use paralel appraoches in IMC they will have to be further apart (redhill has parralel runways quite close together but they are visual runways only)-possibly even min radar separation distance apart (3 nm)-but since that isnt really a starter in the UK I don't suppose anything is laid down.