Just an Observer,
You are correct.
When I was at BA we has a PSA agreement to cover to cost of providing ID100's. That means that tax was paid by the employer not the employee. (I've been out of BA for 3 years so this may have changed)
ID 90's were judged to be non-taxable as the cost to the employer was covered.
Whether a benefit is contractual or not does not impact it's tax impact. The question is whether the benefit is remuneration for employement, e.g if my employer writes off a loan to me, full tax with have to be paid on it.
If this were not the case then many of us would receive substantial "non contractual" benefits, especially when faced with a 60% marginal tax rate.
For those of you with a masochistic tendency start here
Employment income: general: table of contents
and look through the benefit in kind rules