A 25.25m (83ft) long so-called superlorry has been blocked from being driven on public roads by police in Lincolnshire.
The new longer vehicle was being driven from the headquarters of owners Denby Transport, in Lincoln, when it was stopped earlier.
Police said the vehicle was unlawful due to its length.
Denby Transport said its lawyers believe the lorry complies with all the current regulations.
A spokesperson for Lincolnshire Police said: "There are a set of 'construction and use' regulations within British law which cover the use of motor vehicles on UK roads.
We're trying to clarify and test the law - we're not trying to flout it."
Dick Denby, Denby Transport
"These include regulations on length, width and towing capacities of various classes of vehicles.
"If the Denby road train falls outside these definitions then it will be deemed to be illegal on UK roads.
"Therefore Lincolnshire Police will be enforcing the law and stopping the road train to investigate any... offences which may be found."
By comparison, a normal articulated lorry is 16.5m (54ft) long and a "bendy-bus" is 18m (59ft).
The lorry's owner, Denby Transport, wants to bring it to Britain's roads because it says that for lightweight goods such as cereals and aluminium cans, conventional lorries run out of space before they run out of weight.
The new lorry would be able to take more of these goods, even though it would still have to respect the UK weight limit of 44 tonnes.
The company has been working on the project for nearly eight years.
Denby's lawyers said it complies with all the current regulations.
The government disagrees, saying it is illegal and that it will not be allowing longer vehicles on the roads for the foreseeable future.
Dick Denby, from Denby Transport, said: "We're trying to clarify and test the law - we're not trying to flout it.
"If the law decides they are illegal we'll pull it off the roads. If the law decides they are quite legal, everyone who wants one can have one."
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.