This looks to be one of the house spiders, Tegenaria sp. these are common in sheds and garages and occasionally in cooler undisturbed parts of our homes. They are more commonly seen in the Autumn when males wonder in search of lady spiders. It is most likely an example that has been disturbed from somewhere, have you been doing any spring cleaning or been up in the loft space?
Anyway, it's harmless and not an unexpected visitor in our homes.