By Carolyn Cohn LONDON (Reuters) -Investment manager Columbia Threadneedle and pension consultants Mercer warned the Bank of England about the impact on pension schemes of recent gilt market moves, they told Reuters on Wednesday. The Bank of England said earlier on Wednesday it would buy as many long-dated government bonds as needed between now and Oct. 14 to stabilise financial markets, amid a slump in British gilt prices following a government fiscal statement last Friday. Columbia Threadneedle had a “fiduciary duty” to its clients to alert the central bank to problems for pension schemes ca…