The trouble with wiring them into the main beam was it'd quite often burn out the contacts in the steering column switch as relays were considered 'the work of the devil', the switches themselves were often made by Lucas, Prince of darkness and finally, most 55W were quickly swapped out for 100W Halogens, shortening the likelihood of failure time by about 80% - and of course, no-one fitted the isolation switch as required in the C&U regs....
Edit: I think the most spectacular one I came across was a Marina van of all things, with a full Cibie array of rally lights up front - all wired into the high beam, at night there was a visible, audible and ozone-creating smellable arcing from the switch which needed a few on-off-on's until the contacts found an unburnt area to pass the harness-warming amps through.... Needless to say, the fuse had been replaced with a 7/16" threaded version!.