Transferwise is a finacial service which allows to transfer money like as banks or services like Paypal do. They charge 2 pounds for transactions up to 400 pounds at a flat rate. If the transfer amount exceed this limit then a fees of 0.5 percent is attracted. The company claims they have only a 1/8th fees than that of a bank transaction.
As the service is regulated by the Finacial Conduct Authority we can assume it is safe.