David Buxton, head of banking at Sainsbury's, said the bank was trying to get the balance of its mortgage proposition right across four factors: price, distribution, service and policy.
He said the bank would soon be looking at the last of these, which would involve considering issues such as lending to the self-employed.
Mr Buxton said: "From pretty much nothing in April last year we have rolled out to 40 per cent of the broker market and we have got coverage across pretty much all of the lending segments.
"We have got price, distribution and service but policy is also really key.
"It is about us finding the right mix. We have got to be there or thereabouts in all four of them and that’s the real trick for us.
"We have made great strides in trying to make ourselves competitive by offering that full range of products.
"The focus has been on distribution. The bit we have taken more time to develop is our execution-only policy. We are hoping quarter one or two."
Sainsbury’s Bank was historically part owned by HBoS, which later became Lloyds Banking Group.
From 1997 until 2004, it sold mortgages through its partner Bank of Scotland.
Sainsbury’s took full ownership of Sainsbury’s Bank in 2014 and in April 2017 the lender expanded into mortgages as part of "strategic priority," the lender said.
In May the lender entered the buy-to-let market offering products available only through its network of brokers.
When asked about whether Sainsbury's mortgages were aimed at the supermarket's customers, Mr Buxton said: "If you take mortgages out of the equation, our plan is to be the bank to the Sainsbury’s shopper.
"Mortgages is a bit different. It absolutely has that same aim but we want to stand out on our own two feet as a lender in our own right.
"We have got onto all of the panels we wanted to be on today. We are absolutely where we want to be on business volumes.
"If brokers weren't using us, that would tell me something wasn’t working."