A company purchases a machine for $\pounds 100,000$ on $1$ January $20$X$5.$ The machine has an estimated useful life of $10$ years. On $1$ January $20$X$8$ the company enhances the machine by adding additional software controls costing $\pounds 40,000.$ These are expected to have the same remaining useful life as the machine. What is the additional annual depreciation on the machine?