I do try to be aware all the time of cyclists, but with the best will in the world they can and do surprise you being suddenly and instantly alongside very close to the car.
It is not acceptable to arrive suddenly on the nearside rear and expect everyone to know you are there, the only one who would know is the driver
behind you.
If you had been stationary and the car overtook your position I would expect the driver to know your whereabouts, but not if you arrived on the scene when the car was already in position at the roundabout.
Ramble I must pop along to see what this 'exciting' roundabout gets up to
