High beams slow to respond?

It sounds like a typical relay problem. Open the hood (bonnet) and pop the lid open on the fuse box. turn the lid around and locate on the map the high beam relay. Have someone in the car to turn the lights on/off and low/high beam. At the same time do wiggle test on the relay (move it repeatedly sideways). If you get any effects, just replace the relay, otherwise you might look at possible light switch on a short circuit, bad ground. If you get nothing by yourself, get a mechanic to look at it.