Neil Woodford: A victim of his own success? But in recent years Mr Woodford has not just had to wrestle the challenging economic conditions to keep his stellar returns on track - he has also had to deal with a wave of new money flooding into both funds. Since the financial crisis (September 2007) his Invesco High Income fund has grown from £7.5bn to almost £14bn today. The Invesco Perpetual Income fund has jumped from £6bn to £10.7bn. At present his funds have over 30pc in the pharmaceutical sector, most notably in the likes of GlaxoSmithKline and AstraZeneca. Both stocks have delivered solid share price returns in recent years and both still provide decent yields at 5pc and 5.7pc, respectively. But should Mr Woodford want to sell out of these stocks it would not be an easy task. The funds have grown so large in recent years that it now takes a long time to dispose of the giant quantities of shares in his larger holdings. For instance, earlier this year Mr Woodford sold his entire stake in Vodafone. But the process is understood to have taken several months. Fund managers who have less money to run can buy and sell stocks at a much quicker pace - and so snap up fleeting opportunities as they arise. Over the past couple of years Woodford has continued to provide strong returns to his investors. The High Income fund has delivered 42pc and his Income fund has returned 41pc. By comparison, the average UK income fund has returned 35pc. But in terms of income Mr Woodford's performance has underperformed. Over the past two years, the High Income fund has underperformed the average market yield by so much that it was in danger of being kicked out of the Investment Management Association's UK Equity Income fund sector. This is because it failed to produce a yield worth 110pc of the FTSE All Share index over the past two years. Funds that underperform over three years are ejected from the sector. In April, Mr Woodford's Edinburgh Investment Trust also fell out of the top ten of highest-yielding investment trusts after its yield fell below 4pc. Due to sheer size, it would prove difficult for Mr Woodford to overhaul both of his funds in order to boost these yields. A leading investment house - Sanlam Private Investments - downgraded both of Mr Woodford's flagship funds earlier this year for this very reason. The [size of the] assets under management has led the portfolios to become very focused in many of the very large stocks in the market. We would prefer managers who are able to be more pragmatic in the face of swiftly changing circumstances and therefore place sell recommendations here," said the firm. Mr Woodford will continue to run both his funds until next April. His successor - Mark Barnett - has a solid track record of his own and has in fact produced better returns than Mr Woodford over the past five years. However, it will be a major challenge for him to take on such a large portfolio, as he has little experience with the size of funds that Mr Woodford is handing over. Mr Woodford will be launching his own asset management company after he leaves Invesco Perpetual next April and the money once again is likely to follow him. kyle.caldwell@telegraph.co.uk