Britain's oldest investment trust, Foreign and Colonial, saw a sharp drop in its net asset value (NAV) per share during 2011 although income increased.The NAV per share dropped 6.7% compared to 2010, to hit 322.86p by the end of December, over the same period the share price dropped 6.8%.It's not all been bad news for investors, however, as Foreign and Colonial has continued its policy of increasing dividend; the total payout will be 7.1p per share, an increase of 5.2% over 2010, and above the 4.8% retail price index for 2011.The group says income was strong through the last 12 months with the largest contributions from the resumption of dividends by BP and a special dividend from Vodafone. Net revenue per share rose 20.1%. Investment trusts gauge their performance against benchmarks, Foreign and Colonial's is calculated as 40% from the FTSE All-Share index and 60% from the FTSE WI World index. During 2011 F&C's net asset total return was -4.8% compared to the benchmark result of -5.2%.Foreign and Colonial shares were down 0.4% by 09:14.BS