N.B. if you buy a cheap one from Asda, keep the receipt and guarantee in a safe place, i usually put the receipt in the box and stack it on a shelf in the garage, then i know where they are when needed.
The slots are made (as a lot of toasters are these days) for squareish loaves, so are not very deep. Warburton Wholemeal, for example, I begin toasting upright for about 45 seconds, until it shrinks a little. Then I lie it on its side and carry on toasting.