Taxiway clearance is defined in the license for most UK aerodromes and for most the geometry must guarantee that gear remains on the defined surface with either pilot over the yellow line for all types approved for the aerodrome, so you can usually rely on staying on the concrete if you follow the lines.
A full 90 degree turn on is, IMHO, counter productive. Extra tyre wear/damage, more torsional stress for gear (especially on bogey types) and as anyone who operates out of LHR or LGW will know a very, very high price in occupancy and thus capacity/congestion. The risk of coming to grief on account of 10-20m? I would say miniscule.
I use and train that a comfortable moderate turn typical of a 90degree turn on a large taxiway does the job.
As for those who seem to be doing the shocked maiden aunt act at those who don't know the exact line up allowance, it would be worth taking a realistic view that there is a mountain of information that is far more likely to hurt you through ignorance. Claiming that accurate knowledge of this figure is some kind of absolute is ridiculous, concentrate on the stuff that kills people every year.