Many local pharmacies with vaccine stocks have a walk in service for flu jabs. No appointment needed. For example Medicos next to the Jenner Health Centre. And the pharmacy in Woolstone Road. Helps if you you have your NHS number. Free for over 50’s.
Recommend Medicos where I had mine yesterday. Do not recommend Boots who changed the appointment for a time I could not make and could not rearrange.
Our local pharmacy opposite Budgens is advertising flu jabs all over their window. If I have to go in there thr pharmacist asks as soon as you go in!
I had mine done at my GPs, & my husband is having his done there this Friday.
Actually allowed in the GP surgery 
For those going with Boots…(I have to use them for my workplace flu voucher scheme)
I’ve had an appointment cancelled at Forest Hill due to sickness. The next available appointment was in mid-November. I’ve checked with another branch near work in Central London and they’ve had almost free choice of appointments from the next day. So it’s worth shopping around.
It’s certainly worth popping into a pharmacy if you’re out and about and asking. I popped into the one at my local ASDA and was sorted out immediately.
It seems like you do better dealing with a Boots branch directly as the online booking service hasn’t been offering appointments before 1st November for a couple of weeks. And yet I’ve heard of people getting appointments sooner when they’ve gone into a branch.
Work pay for flu jabs and I had mine at a central London Boots last week. I booked it the day before.