Indeed, there is actually no legal limit on the height of a truck in the UK, though by ‘custom and practice’ 4.9 metres has been adopted as the maximum height of a trailer. This has enabled many British businesses to double-deck their lorries, gaining extra cubic capacity vertically.ther double-trailers will have heights less 4.8 metres and hence significantly lower carrying capacity ratios. Another constraint on this ratio is the vehicle weight limit, currently 44 tonnes for a 6-axle articulated vehicle and 40 tonnes for a 5-axle lorry.