My washing machine is 5m away from the water mains copper pipe/valve. I've currently got a long blue inlet hose connecting the washing machine to the copper pipe/valve.
Is this OK or should I get more copper pipe added and then use a shorter blue in let hose to connect the 2?
Inlet hose length can be as long as you want. Any plumber should do their best to make it as small as possible purely for good workmanship, but I certainly wouldn't go moving one for the sake of it if you already had a long hose on it.
Waste hoses are a different story. If you ever have to extend your hose you need to check the instructions for maximum pump distances. Even then the shorter the better.
If your long inlet hose is in one piece, you should be fine.
I had a similar situation in a holiday cottage when, unknown to me, the washing machine installer used two hoses connected in series. Some years later a damp patch started to appear in a room below. Upon investigation there has been a slight leak from the join in the hose, over a long period of time, which had spread over a big area affecting the chipboard floor and base of the kitchen cabinets. Quite a mess! ☹️