So two posts and two different answers look keo and speedplay.
They are both sound answers. Speedplay do a track specific version of their pedal which is used at the highest levels, as is the Keo. The trouble with Speedplay is that they need an adaptor to mount to normal 3-bolt shoes, so you lose much of the advantage of low stack height and stiffness, but with custom drilled shoes they seem to be well regarded.
Keo is very widely used, including on the hire bikes at Calshot, so you have the advantage that you're likely to be able to ride other people's bikes more easily if you have Keo cleats on your shoes.
They are both sound answers. Speedplay do a track specific version of their pedal which is used at the highest levels, as is the Keo. The trouble with Speedplay is that they need an adaptor to mount to normal 3-bolt shoes, so you lose much of the advantage of low stack height and stiffness, but with custom drilled shoes they seem to be well regarded.
Keo is very widely used, including on the hire bikes at Calshot, so you have the advantage that you're likely to be able to ride other people's bikes more easily if you have Keo cleats on your shoes.