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That depends on whether you need to sell the bond before its maturity date. Supposing it is a 1 year bond, if you hold it for the full year you get your £100 back. If you need to sell early, then you might get less back if rates have risen.

A money market fund operates differently from holding individual bonds and aims to provide you with the ability to sell at any time without a loss --- but the monthly interest paid out will fluctuate according to market rates.