LONDON, May 26 (Reuters) - The number of mortgage approvals for UK house purchases rose an annual 15.5 percent in April to the highest level this year, industry data showed on Wednesday. The British Bankers' Association said the number of loans approved for house purchase rose to 35,729 last month from 35,044 in March and 30,649 in April 2009. However, the number remains well below levels of ...