You should pull up and remove weeds by hand as and when they appear. If it is a regular problem, you might need to reseal the paving. In extreme cases, the sub layer itself may need to be re-laid. You can use weed killer, however some paving can be discoloured by stronger weed killers.
Carnforth
Carnforth is a town and also civil church near Lancaster in the north of Lancashire, England, situated at the north eastern end of Morecambe Bay. The parish of Carnforth had a population of 5,350 recorded in the 2001 census, as well as kinds part of the City of Lancaster. The 2011 Census measured a population of 5,560. As a result of the closeness of the coast and also the hills, Carnforth is a popular base for walkers and bicyclists discovering the area. The River Keer, the West Coast Main Line (WCML), the A6 and the Lancaster Canal go through the town. The M6 freeway passes simply to the east, linked to Carnforth by the A601(M). The name "Carnforth" is believed to stem from its old function as a ford of the River Keer on which it is positioned. Gradually the descriptive name "Keer-ford" might have changed into the contemporary "Carnforth". An alternative explanation is that the name derives from 'Chreneforde' and is Anglo-Saxon in beginning, as pointed out in the Victoria County History of Lancashire.