OBSR, part of Morningstar, has lowered its rating on the BlackRock UK fund to 'A' from 'AA', citing the recent manager change.

Nick Little has taken over from Mark Lyttleton. OBSR said it "is comfortable with the new manager's investment philosophy and process which it believes is consistent with the requirements of a benchmark aware fund, but believes an A rating to be a better reflection of OBSR's conviction at the current time."

OBSR has also withdrawn the 'AA' Rating from Henderson High Yield Monthly Income fund and removed it from its ratings service.

This follows the announcement of the fund's merger into the Henderson Fixed Interest Monthly fund. Both funds have been managed by John Pattullo and Jenna Barnard since August 2011.

"We do not anticipate significant further fund management changes as a result of the planned merger and we have therefore maintained the OBSR AA Rating on the Henderson Fixed Interest Monthly Income fund. This reflects our continued conviction in the managers' ability to use their experience to capitalise on their strategic outlook for different segments of the fixed income universe and consequently to deliver an attractive total return for investors."