It's a bit unfortunate you didn't ask for this advice when you planted the hedge - the routine for hedging with this plant (and others) is to cut back when planting, by half if the plants were bare root, or two thirds if they were in pots. In the second year, they should be lightly trimmed about 4 times a year, and as the hedge matures, twice a year. The shape of the hedge should always be a bit wider at the base than at the top, to encourage growth at the base so you don't have gaps appearing.

Now that yours have reached five foot, its possible gaps are already appearing - I'd reduce the top by at least a third, and trim the sides so that they slope inwards.

Thanks for the advice. So I should remove the top third off the plant? I'm not sure what you mean about trim the sides inwards??

You eventually want to end up with a hedge that's a bit wider at the bottom than it is at the top - this means that light will still reach the lower parts of the plants, so they'll still produce green growth at the base. Without seeing the plants, I can't tell if there's enough lateral growth (side growth) to clip back in such a way, but that's generally what you're aiming for as time goes by. And yes, I'd take a third off the top now.

Hi there. A year on and the plants have grown really well. I took heed off the advice above but feel the bottom hasn't bushed out well yet. The plants are at the desired height so do I cut the top stem off now and let them spread out?