[Dimtree]

I think you're missing the most common reason. Up to 65% of the global population is lactose intolerant to a degree.

https://ghr.nlm.nih.gov/condition/lactose-intolerance

[lawlorino]

As a counterpoint that's not uniformly distributed globally, the incidence is much lower in Northern Europe including UK where OP is from.

[Dimtree]

As a counter-counterpoint, you assume OP's ethnicity is Northern European just because he lives in the UK.

[n4r9]

That might be the most common reason globally, but not necessarily in the UK where only 5% are intolerant. Many of those can tolerate small amounts such as you'd put in tea/coffee.

[dragonwriter]

Lactose-free dairy products are readily available.