Spa treatments in the Gatwick Clubhouse

Can you only book spa treatments when you arrive at the clubhouse? Is there any way of booking them in advance?
I have heard of people being unable to have a spa treatment as all the morning appointments have been booked by those on earlier flights. My flight will depart at 11.15am so I would need an early appointment. Is it just first come, first served and tough if it's fully booked? (Won't really be a great problem to be fair).
Thanks

Yes, it's first come first served on the day. If it's busy slots do book up quickly so get there early if you want one.

Great, thanks gumshoe.

I got there at 7am for a 10:45am flight and managed to get an appointment easily. The free head massage was really good and £15 hot stone massage was as well.

Thanks LucyLu. I'm hoping to get there fairly early to make the most of the clubhouse experience.