Mr Kingston said the drop would be due to the "hostile regulatory environment" for Sipps.
This hostile environment is due, he says, to the requirements last year by the Financial Services Authority for higher capital adequacy requirements and standards.
{desktop}{/desktop}{mobile}{/mobile}
There are currently around 160 different Sipp providers in the UK with 117 having written business within the last six months.
Mr Kingston said: "The regulator delivered unambiguous messages in 2012 about the standards it expects from Sipp providers. Implementation of these starts this year with a new, greatly increased capital regime expected to follow in 2014.
"This regulatory environment will make it increasingly difficult for Sipp providers to survive if they do not already have sufficient scale and if there's insufficient money to meet the new capital requirements there's also insufficient investment to buy that scale by acquiring other providers."
But Mr Kingston says the drop in providers need not be perceived by advisers as a negative outcome.
He said: "Less choice in the Sipp market is actually likely to deliver better outcomes for both advisers and investors.
"Some providers will continue to offer niche and specialist services as well as access to more esoteric investments, but advisers will ultimately have more confidence that the provider they choose is sufficiently strong and has the necessary processes and controls in place."