'Mummy porn’ book, Fifty Shades of Grey, continues to keep staff at Mackays printers in Lordswood busy with the news that it is now outselling the Highway Code – and is the best-selling British book of all time.

The novel, one of an erotic trilogy, has now sold more than 5.3 million copies.

Staff at the printers on the industrial estate in Badger Road have been working around the clock to keep up with demand for the raunchy read.

It has topped the number one slot for the 16th week running, smashing Dan Brown’s record for The Da Vinci Code.

Mackays’s marketing manager Dino Bishop said "We have already done 28 reprints and there’s no sign of it easing off."

Meanwhile the other two books, Fifty Shades Darker and Fifty Shades Freed, have sold £3.6 million and £3.2 million respectively. Sales are still soaring at Waterstones in Chatham High Street.

Book seller Katie Blench, 18, said: "Just when you think sales are retreating one day, we sell 30 the next day. It’s still mostly middle-aged women and young girls buying it, but some men too."

Mackays printers featured in a Channel Five documentary on Wednesday night, Fatima Whitbread – Growing Up In Care: My Secret Past. Sequences were filmed there in May, when the Olympic silver medallist visited to watch the printing of her autobiography, Survivor.

Former international footballer Neville Southall went to the works on Wednesday to sign copies of his autobiography, The Binman Chronicles