Finish Dishwasher Machine Cleaner | Original | Pack of 8, 250ml Each |Deep Cleans and Helps to prolong life of your dishwasher - £12.05 S&S

In an empty machine place a bowl containing white vinegar, which can be bought for less than 40p. Put the machine on a hot cycle if possible.
The water blasted up by the machine fills the bowls and helps distribute the vinegar. Don't just pour it in the machine at the start as most do a drain cycle to start.
If you want to really make sure its clean, and that all organisms are dead, go to your local Eastern European shop and buy the 20% vinegar, around £2 per litre, and use 500ml for the machine. (edited)

The problem with vinegar for everyone who says vinegar is your machine and plates then smell of vinegar for days afterward. Vinegar also doesn't deal with congealed fats, or other biosolids in your machine. (edited)