Battle Health Centre is not on Bookable yet, so you need to register through the NHS website. You can also book online with a GP surgery nearby.
No. You have the right to register with a GP surgery even if you do not have proof of address, ID or an NHS number. This includes people who are new to the UK.
If you need urgent help, call 111 or go to 111.nhs.uk. If it is a life-threatening emergency, call 999.