Although there is often a great deal of food, in the outdoors, about for our small, very fast rodent there is a progressively shrinking choice of suitable places for them to live. I know it’s a big wide world so why my your house? Putting it in a few simple terms: given the choice of a nice warm, weather proof and often predator free place to bring up their young is often preferable. The more of their natural habitat we destroy with building and development the less choice they have. Why hunt for suitable food sources when they can comfortably live on the crumbs from under your toaster?
They will eat anything they can get hold of including, dog food, cereals, candles, seeds and soap. Generally speaking they do not eat items such as paper/cardboard, cavity wall insulation or carpet they chew and shred it to be used as bedding.
For a closer look into mice and other small rodents found in the UK: https://www.woodlandtrust.org.uk/blog/2017/07/types-of-uk-mice/
to know more about how to identify signs of a mouse infestation in a building check out: https://www.thebalance.com/how-to-tell-if-you-have-mice-in-your-rental-property-2125265
It’s often difficult to discover you have mice initially as they are general nocturnal and will stay away from people given the chance. Once you have seen damage from these small ‘house guests’ it normally indicates that they have been there a while. Unlike rats, mice will leave their dropping wherever they have been as they have little control over this end. Many people either hear the scuttling or scratching at night or see the droppings before they notice substantial damage.
The rule of thumb is: You never only have 1 mouse.