Aegon employs 2,000 in Edinburgh and Mr Grace's comments come amid concerns in the sector about the tax and currency implications for cross-Border businesses in the event of a vote for independence.
Speaking yesterday Mr Grace said: "Ninety per cent of our customers are in England and Wales, they don't want to take currency risk, so we have got contingency plans."
Fellow Edinburgh-based insurer Standard Life has already disclosed it has contingency plans to move the registration of 180 entities from Edinburgh to London.
Mr Grace added: "Aegon UK's life company is registered in Scotland but we are part of an international group and have customers across the country.
"In the event of a yes vote, we'd consider the location of where we register our companies."
But only a "relatively small number" of customers had expressed concerns ahead of the referendum, he said.
Mr Grace was reporting a tenth successive quarter of earnings growth at the Dutch insurer's UK arm, with underlying earnings up 33 per cent to £32 million, largely due to the group retaining customers better.
He said: "The company's earnings are on the right track and are higher than at any point in 2013, we believe the earnings growth reflects the strength our corporate strategy."
Three months ago Aegon revealed that the government's 0.75 per cent charge cap on workplace pensions would cost it up to £25m a year, while it will also be hit by the loss of annuity sales from the arrival of new pension freedoms next April.
Mr Grace said Aegon was similar to Standard Life in that it retained only around 30 per cent of its pension customers as annuity buyers, did not compete to sell annuities in the open market, and had a strong offering in the alternative option of pension drawdown.
Aegon now faces an increased technology spend in the next quarter to adapt its online platform to the new drawdown rules.
Mr Grace commented: "Our platform is state of the art technology developed recently so it is pretty easy to adapt."
The group was a late entrant into the platform arena with its retirement choices platform for advisers fully launching early last year. Since then Aegon has built onto it direct to consumer and workplace portals which it says will enable it to exploit fully the new flexibilities in individual pensions and the opportunities in auto-enrolment.
Assets on the platform have now reached £2 billion, which compare with £21bn at Standard Life and £7bn at independent start-up Nucleus, which is also in Edinburgh.
That has prompted some in the industry to question whether Aegon is too late to win a big enough market share, but Mr Grace said: "Ours is the only platform in the UK that will have three separate markets sitting on top of it ...we are a first mover and have got a unique positioning."
He added: "It's a bit of a technology war at the moment but we are confident that we are the only platform that plays in these three markets."
Mr Grace said growth of the platform was deliberately slowed between October last year and March as its operations centre was being transferred from Bath to Edinburgh.
He went on: "Much of the nation's wealth is concentrated in the hands of the over 50s and new flexibilities mean these people have a range of options as to what they do with their savings.
"We are on a mission to get the UK ready for retirement and are helping employers, customers and their advisers to achieve this."
Aegon said the business added 49,000 customers in the second quarter, up from 43,000 in the first, partly due to the platforms but also to auto-enrolment, where new schemes enrolled were up from 245 to 600.
It said: "Many of the companies Aegon has worked with on auto-enrolment are introducing pension provision to their staff for the first time and Aegon expects engagement rates to be high."
The pensions business moved from a £3m loss in the second quarter last year to a £4m profit, though the life division's earnings were down nine per cent at £21m.