House price annual inflation was 5.8% in England, 2.5% in Wales, 2.9% in Scotland and 10.5% in Northern Ireland.
The pace of annual house price growth increased slightly across the majority of the UK in May 2015.
Annual house price increases in England were driven by an annual increase in the East (9.3%) and the South East (8.2%).
Excluding London and the South East, UK house prices increased by 5.2% in the 12 months to May 2015.
In May 2015, prices paid by first-time buyers were 5.1% higher on average than in May 2014. For owner-occupiers (existing owners), prices increased by 5.9% for the same period.
Alex Gosling, chief executive of HouseSimple.com, said: "Despite the rate of price growth slightly decelerating, demand has remained constant.
"A shortage of stock during the pre-election uncertainty stilted the market, however the flurry of properties which have come on since the election's clear result have coincided with a strong return to confidence.
"Both sellers and buyers are trusting the market more, prompted by steady economic growth, better employment prospects and a boost in earnings.
"But it is worth noting that vendors may consider it to be a sellers' market, but buyers are not making the same mistakes of the last boom, as they remain sensitive to both price and affordability."
