If you want your coin mech to accept any coins that are different to what it's currently taking, then the coin mech will need to be re-programmed, as will the 10s of 1,000s of coin mechs up and down the country, costing the industry millions when it's already in difficult times. The same thing applies to note acceptors when a new style note is brought out. Whilst the denomination may be the same, the size, shape and metal content, and therefore the electrical resistance, of new coins will set them apart from the old coins, as will the various counterfeiting measures built into our notes. If you don't want the expense or hassle of re-programming, just use £1 coins, but sooner or later, they'll change them too and screw us all.
We are having to reprogamme SR5E Coin mechs atm to the latest firmware for it to accept new coins! Dont know about all the other coin mechs atm only time will tell when we have to update these!!