The double-digit house price growth recorded in May followed a 7.1% annual increase recorded in April, Nationwide Building Society said.
Across the UK, property values hit a new record average of £242,832 – up by £23,930 compared with 12 months earlier.
The figures prompted debate among experts about whether the house price boom could be followed by a bust.
House prices were up by 1.8% month-on-month following a 2.3% increase in April.
Robert Gardner, Nationwide’s chief economist, said: “The market has seen a complete turnaround over the past 12 months.
“A year ago, activity collapsed in the wake of the first lockdown, with housing transactions falling to a record low of 42,000 in April 2020.
“But activity surged towards the end of last year and into 2021, reaching a record high of 183,000 in March.”
He said the spike in sales was helped by a stamp duty holiday, which was due to end in March but later extended.
He added: “A lot of momentum has been maintained. Our research indicates the extension to the stamp duty holiday is not the key factor, though it is clearly impacting the timing of transactions.
“Amongst home owners surveyed at the end of April that were either moving home or considering a move, more than two-thirds (68%) said this would have been the case even if the stamp duty holiday had not been extended.
“It is shifting housing preferences which is continuing to drive activity, with people reassessing their needs in the wake of the pandemic.
“At the end of April, 25% of home owners surveyed said they were either in the process of moving or considering a move as a result of the pandemic, only modestly below the 28% recorded in September last year.
“Given that only around 5% of the housing stock typically changes hands in a given year, it only requires a relatively small proportion of people to follow through on this to have a material impact.”
Of those moving or considering a move, a third (33%) were looking to move to a different area while nearly 30% were doing so to access a garden or outdoor space more easily.
More than a third (36%) said they were more likely to consider enhancing their home as a result of Covid-19, with nearly half (46%) of these looking to add or maximise space.
Mr Gardner added: “It is interesting that around a third (35%) of home owners looking to enhance their home cited an intention to improve energy efficiency or reduce the carbon footprint of their home – a key shift if the UK economy is to become carbon neutral, given that the housing stock accounts for around 15% of the UK’s carbon emissions.”
Samuel Tombs, chief UK economist at Pantheon Macroeconomics said: “The upward pressure on prices looks set to remain strong over the coming months.”
Mark Harris, chief executive of mortgage broker SPF Private Clients, said: “Buyers wanting more space, trying to take advantage of the extended stamp duty holiday and the lack of supply are all pushing values upwards.”
Jeremy Leaf, a north London estate agent and a former residential chairman of the Royal Institution of Chartered Surveyors said the figures “reflect market activity in the last few months when prices were turbo-charged by the extension of the stamp duty holiday”.
He predicted house prices “will soften but not correct and next month’s index is likely to show strong but more moderate growth”.
Anna Clare Harper, CEO of asset manager SPI Capital, said: “Some will see 10.9% annual growth in the year to May as a boom, to be followed shortly by a bust, but what tends to happen in the housing market is different from other purchases and investments.
“The consequences are also different, and significant politically, economically and socially.
“In other sectors, low consumer confidence tends to reduce consumer spending, and low investor confidence tends to cause emotional selling. It is different in the housing market because homes are ‘essential’. We all need a roof over our head, so people tend not to sell unless they really need to.
“With interest rates low, it can be cheaper to pay a mortgage on an equivalent property than to pay rent, once you have put down a deposit. So a mass sell-off seems unlikely – in the absence of significant interest rate rises.”