Made an account just to reply to this as I feel very strongly about it!
I requested to be out of the classroom as of Christmas (35 weeks) due to my concerns over term-holiday mixing and the inevitable spike it would cause.
It seems the biggest battle was HR as they didn't agree to paying for supply before my mat leave started.
Advise number one: DO NOT accept taking mat leave early. Your employer has to make reasonable adjustments to accommodate your needs.
I had written confirmation from my midwife and consultant to back-up that I should be out of the classroom from Christmas.
HR countered this with a (joke of a..) risk assessment that included gems such as "masking tape a 2m box around your desk so the children know to socially distance from you". I teach 6-year-olds in the world's smallest classroom...
Anyway, eventually, only a GP note would be taken seriously by them. A GP who I'd never met, knew nothing about my pregnancy, but there you go...
They wrote a fit note stating that I must be socially distanced in the work space with immediate affect (this was two weeks before Christmas) and therefore should not be working within a whole classroom setting.
HR can't argue with that...
Speak to your union. Speak to your GP. Know that what you're asking for is reasonable and appropriate given the situation you're in and don't let ANYONE tell you otherwise.
You can do it in a non-confrontational way with your head. Just go down the route of "I was seeking the most up-to-date advise to help you because I know the government advise is a bit hazy.."
Good luck!