He has been told by the police that his car was stolen during a test drive last year. Mr Marriott's predicament is aggravated by the fact that he has spent pounds 700 on the car since he bought it.
He was first alerted that there might be a problem by the Driver and Vehicle Licensing Centre, which spotted a discrepancy in his registration documents.
Mr Marriott says: 'I bought the car in October last year and received registration documents within a couple of weeks. Everything was correct and registered in my name.'
Mr Marriott, an assistant cashier who lives at Enfield, Middlesex, and the dealer who sold the car seem to be victims of ringing.
This practice involves giving a stolen car a new identity by using number plates or other parts from a different car of the same model. These are usually, together with registration documents, brought from a scrapyard.
The process can involve changing the engine and chassis numbers or even welding parts from different cars together. The stolen car, with its new identity, is
then sold to an innocent buyer.
Buying a second-hand car can prove a risky business. The problem is that the registration documents handed over do not prove ownership of the vehicle.
The DVLC warns: 'The registration document should be given to you when you buy the car. Remember, this document does not prove legal ownership.
'Before buying a vehicle you should satisfy yourself that the seller either owns it or is entitled to offer it for sale. Ask to see a bill of sale in the seller's name or other evidence such as a hire purchase discharge document.'
The general position in law is that a purchaser cannot legally own a stolen car. However, car dealers' transactions are governed by the Sale of Goods Act 1979.
This states that it is an implied term of any contract that the seller has legal ownership of the goods. If this turns out not to be the case the buyer can sue him for breach of contract and get his money back together with the cost of improvements. He can also try to recover from the true owner the money spent improving the car.
The position is less fortunate for those who buy from a private seller. If the car has been stolen, often the seller has disappeared by the time the fraud is recognised. If the original owner turns up and demands the return of his car there is little the buyer can do.
Buying a car from a dealer is less fraught with danger than buying from a private seller. The Sale of Goods Act requires that any car sold by a dealer to a consumer should be of merchantable quality and fit for the purpose.
If the car is found to have a serious defect which becomes apparent soon after purchase the buyer can demand his money back.
In a private sale no such warranties are implied. The onus is on the buyer to inspect the car carefully. The seller will only be liable if he has misled the buyer as to its true condition. It is, however, an offence under the Road Traffic Act to sell a car in an unroadworthy or unsafe condition.
The AA information service advises those buying cars to ask about the vehicle's history, including its mileage, the number of previous owners and whether it has been involved in any accidents. The buyer should also ascertain whether there are any finance agreements outstanding.
Geoff Williams, a general sales manager with Mann and Chapman, franchise dealers for Volkswagen and Audi at Little Chalfont, Buckinghamshire, says: 'Buying from an established dealer is always the safest policy. I would advise anyone thinking of buying a car privately to take along a friend who knows something about cars.
'An alternative is to arrange for an AA or RAC survey. They will detect loads of faults, but at least you know what you are getting.'
Unfortunately for Mark Marriott, his car is not defective but his legal title is.