By Jennifer Sieg House prices have remained“relatively flat” for the third consecutive month in June, down 0.2 per cent, according to new data from Halifax, with London remaining one of the most expensive markets in the UK. According to the Halifax House Price Index, the average house price in the UK is £288,455, with London averaging nearly double at £536,306, up 0.9 per cent from last year. “For now it’s the shortage of available properties, rather than demand from buyers, that continues to underpin higher prices, Amanda Bryden, head of mortgages, Halifax, said. “Mortgage affordability is st…