BRITAIN’s top public schools are being investigated on suspicion of illegally colluding to fix fees. The Office of Fair Trading visited Winchester College, Eton and Westminster School last week. Parents have seen an average fee increase of 10 per cent this year, the biggest on record. The maximum penalty for breaching the Competition Act is 10 per cent of the school’s annual turnover for three years, equivalent to pound;10 million at Eton.