An employee (Vegan) is demanding that we provide a freezer for her to store her specilist food in.

As far as I understand it there is no such duty on an employer to provide such facilities - although I accept there may be certain circumstances where an employee with a medical condition might apply.

Any thoughts or pointers?

Ta

The comparable situations would be provisions for religious groups who may require separate facilities, eg Kosher. Surely the food should be suitablly wrapped by the vegan to prevent the 'contamination' she is seeking to avoid. And why a freezer; do non vegans have access to a freezer?

That's as far as you need to go, any further and you start to discriminate against everybody else. I had a similar probem with someone who monopolised the office fridge because she chose to shop at lunchtime. Not fair on everyone else, and no reason why she shouldn't manage her retail activity to suit the majority. Same with your vegan employee, adaily lunchbox is perfectly adequate.