I found a handy hint online that suggested soaking the knife in white vinegar. This method is for stainless steel knives and cutlery only.
I left the knife to soak in a glass of white vinegar for a while, then I removed the knife from the glass and with a clean dry sponge I scrubbed at the rust at the end of the blade. It took quite a while to get it all off as the rust was diffcult to reach because of the shape of the handle. Be careful not to cut yourself while cleaning the knife.
After the rust had been removed I washed the knife in warm soapy water and then dried it thoroughly.
This method only removes rust, it won't prevent it from happening again in the future.
After I'd finished I decided to reuse the vinegar. I poured some baking soda down the kitchen sink plug hole and down the bath plug hole, I then poured the vinegar down both plug holes. Baking soda and vinegar react with each other and start to fizz, this should remove any soap residue that has built up down the plug holes. After the fizzing had stopped I poured a kettle of boiling water down the plug holes to clear them out.