The ‘Rent-A-Room' entrepreneurs collectively accumulate over £3.9 billion per year in rental payments - an average of £182 per month.
The research shows that there is currently a potential £52 billion of rental income to be made in the UK from renting out spare rooms. However, nine out of 10 people (92 per cent) with a spare room still choose not to rent it out though there are 3.7 million homeowners who have considered doing so.
More than a third (35 per cent) of those who rent out a spare room do so to help out a friend or family member. A further one in five (18 per cent) do so because they need the additional income to meet their outgoings whilst 17 per cent need the money to supplement their disposable income.
Homeowners in the South of the UK accumulate the most amount of rental income from their spare rooms. One in seven (14 per cent) people in the South West and one in ten (11 per cent) of those in the South East rent out a spare room.
Meanwhile Brits living in the East Midlands (4 per cent) are less enthusiastic about taking in a lodger.
Three quarters of UK homeowners would not consider renting out a spare room with more than half of them (52 per cent) not wanting to do so because they don't want a stranger in their home.
One in three Brits (33 per cent) keep the spare room free purposely for guests, 21 per cent do not need the additional income and 21 per cent use the room for storage.
Of the one in four (25 per cent) Brits who would consider renting out their spare room, 11 per cent would do so if they needed to financially and 15 per cent would rent out the room if a friend or family member needed it.
Some 7 per cent would consider it if they could find an appropriate tenant and 4 per cent would do so if they were able to make decent money from it.
The findings also reveal that storage space is the most popular use of a spare room in the UK (37 per cent). In addition, more than a third (35 per cent) of Britons use their spare room as an office whilst just three per cent of Brits use the spare room as a nursery.
Phil Cliff, Director of Santander Mortgages, commented:
"It's interesting to see that so many Brits are weathering the economic storm and showing such entrepreneurial spirit by renting out spare rooms in their home. This can make a real difference to how much money you have left at the end of the month.
"However anyone with a mortgage who is renting out a room should speak to their mortgage lender first to check they aren't breaching the terms and conditions of their agreement."
Matt Hutchinson of Spareroom.co.uk said:
"With so many homeowners renting out their spare rooms, it's time for the Government to think about raising the rent-a-room tax-free threshold, which has not changed since 1997.
"Tax breaks available to homeowners looking to make some extra cash by taking in a lodger need to take into account rising rents and the soaring cost of living.
"The average annual room rent for the whole of the UK is £4,560 and in London it's £7,200, well above the current rent-a-room relief threshold of £4,250.
"This survey carried out by Santander underlines how many homeowners rely on lodgers for vital extra income, but I'm sure many are put off by the prospect of having to fill out a self-assessment form for taxable earnings above the current threshold."
