Your main references would be:

CD143 for public highways - this looks for 2.0m minimum

https://www.standardsforhighways.co.uk/dmrb/search/9b379a8b-b2e3-4ad3-8a93-ee4ea9c03f12

Building Regulations Approved Document M - this looks for 0.9m minimum

https://www.gov.uk/government/publications/access-to-and-use-of-buildings-approved-document-m

The 1.2m is based on theoretical consideration that two able bodied persons could pass within such a width although it is more likely to be related to the clear access required when designing to allow a wheelchair user to swing in to a doorway left or right of a central corridor.

JB - to add to what Roundtuit has said, "DMRB" - Design Manual for Roads and Bridges - applies directly to each of the four national Governments in the UK, but is generally adopted by local authorities.

Essentially for a publicly maintained* highway, you either do what DMRB says or you justify a "Departure from Standards" - which is an exercise that designers generally try to avoid negotiating - the rationale has to be very good.

In your private car park DMRB would not apply but the principles are sound, and considerations for e.g. wheelchair users as, if not more, appropriate.

*There is a distinction between a "public" highway and a publicly maintained highway. A supermarket car park would be a public highway, but not directly subject to DMRB. But then, the supermarket, like you, need to consider the user profile to decide on design criteria.

P

They are considering copying the no pavement parking applicable to London across England

https://www.express.co.uk/life-style/cars/1421970/new-pavement-parking-outside-home-law-rule-fine-penalty

Returning to the original question: the answer is wide enough for your workplace.  These questions keep appearing on the forum and they seem to assume that there is a group of civil servants or related pen pushing parasites  who spend all of there time coming up with ever possible scenario in the workplace  and as a result they have drafted  detailed guidance on each and every topic under the sun or at least in the workplace. Of course they haven’t and its down to the business to decide for themselves what is  a wide enough footpath is.  It might need to be more than 2 m if it is busy route across the site  or somewhere that people manoeuvre loads. Equally less than a metre might be adequate if it is only used occasionally and purely by people exiting their cars.  Do the powers that be want it wider or narrower? Are they trying to fit more cars in or have the bean counters decided that if they save on the cost of a tin of paint, they can earn a bonus this year?