The service was launched in November 2010 with only three advisers and was restricted to members of Which? as well as family and friends.
It will be funded through lender procuration fees with Which? funding the service when no fee is paid.
Some 80% of mortgages it has advised on so far have been deals which pay procuration fees.
The consumer group currently has 12 advisers which are paid on a flat salary but the firm said it would grow this number to at least 20 depending on demand.
A spokeswoman from Which? said:“Following a year of successfully helping our members and their friends and families, we have decided to open up the service to everyone who is looking for mortgage advice, so that we can help all consumers choose the right mortgage.
“We will recruit more advisers as demand for the service grows, to make sure that our customers receive the highest levels of service.”
David Sheppard, managing director at London-based Perception Finance, said: “It is good to see that the Which? offering has proved to be successful as it shows that people do seek out independent advice when taking on a mortgage.
“The important thing is that Which? is seen to advocate advice and support the whole of market sector in its entirety.
“There is room in the market for competition and the service on offer is also key. I would imagine that Which? will provide email and telephone-based advice but there will also be clients that want the option of face-to-face.
“Ultimately the expansion of the service should be embraced by other brokers as a positive sign that the market may be improving albeit slowly.”
Lea Karasavvas, managing director at Prolific Mortgage Finance, said: “I don't see how this differs to many in the mortgage industry at present.
“The majority of brokers I speak to of late are not charging fees and simply taking remuneration from the proc fees simply because of the challenge of dual pricing.
“Commissions are enhanced by cross sales of protection and GI and these cross sales often negate any fee that is payable.
“One thing to note is that according to the Mortgage Conduct Of Bus regulations, you cannot be deemed Independent Mortgage Brokers unless you are giving your clients the opportunity to pay a fee for the advice.
“So Which?'s USP is that it will not charge the client a fee but that means it cannot trade as an Independent Mortgage Brokerage, only an impartial one and this could be of great detriment to an otherwise fantastic proposal.”
David Hollingworth, associate director, communications, at Bath-based London & Country, said: “Whilst many will question whether Which? should be getting involved in mortgage advice, I think it is very encouraging that it clearly appreciates the need for mortgage advice in the current market.
“They clearly have a strong brand behind them, have already marketed that to their subscriber base and it’s no surprise that they are opening that out to a wider audience.
“It obviously remains a difficult market but provision of advice is something that consumers understand is a vital part of securing a mortgage these days – this wider launch only goes to underline that fact.”
