The 2ft 8in high by 8in (80 x 19cm) wide panels housed in typical hardwood frames were found by valuer Richard Bromell in a modest chalet bungalow.
One panel was hung on a wall behind a door, another on the landing with the remaining two in bubble wrap under the bed.
They had been bought by the father of the vendor when he visited Hong Kong more than 50 years ago.
The panels, particularly desirable as a set annotated by poems, are almost certainly by one of the Eight Friends of Zhushan - the key group of Republic period decorators instrumental in revitalising the Chinese porcelain industry after the fall of the Qing dynasty.
The key landscape painters in the group were Wang Dacang (1899-1953) and Wang Yeting (1884-1942) - whose red seal appears next to the poems on all four of these plaques.
Huge multi-estimate prices have been paid in recent months for the best Republic period porcelain plaques by the Zhushan Friends: at Cheffins of Cambridge a figural panel by Wang Qi (1888-1934) took £230,000 in October, while Christie's South Kensington sold a landscape panel by Wang Dacang in November for £300,000.
The sale of the set of Wang Yeting panels at £420,000 on February 14 came exactly a year to the day after Charterhouse achieved their house record of £460,000 for a maiolica istoriato charger c.1540 decorated with The Feast of Herod.
"I never thought I would get close again," Mr Bromell told ATG.
The buyer's premium was 19.5%.