i apologise....apparently, you can take paid time off to attend antenatal appointments (antenatal = before birth), but obviousloy have to go into work afetrwards.... the gov.uk site states:
Pregnant employees have legal rights - including paid time off for antenatal care, maternity leave and maternity pay.
Pregnant employees have 4 key rights:
paid time off for antenatal care
maternity leave
maternity pay
protection against unfair treatment, discrimination or dismissal
‘Antenatal care’ isn’t just medical appointments - it can also include antenatal or parenting classes if they’ve been recommended by a doctor or midwife.
Employers can’t change a pregnant employee’s contract terms and conditions without agreement - if they do they are in breach of contract.
It’s illegal for employers to refuse to give pregnant employees time off for antenatal care or refuse to pay their normal rate for this time off, but fathers don’t have a legal right to time off to accompany their partners.
with this in mind, i suggest you go back to your employers and say, ahem....it is my right to do xyz.....how do you wat me to do this? with such info, you should be able to come up with some kind of compromise as to how you can attend yur appointment and go back to work on the same day (if that is your choice), or that they take the time off your working hours and negotiate some way that recognises your right to attend these appointments. it cannot be taken as annual leave or flexi time (or anything else for that matter). they must know this and are trying to blackmail you into working instead. it is obviously, therefore, not your problem how they cover these hours, and is something that they have to cover/organise themselves into managing. you say you have given as much notice as possible - go back to them with this information and stand firm....please igtnore my other answer (i can only blame the drink!)
https://www.gov.uk/working-when-pregnant-your-rights