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You can use this site if you can get the MOT test number (no reason why the seller cant give you an old one)
This will only work IF the MOT station that was used to take the test uses a computerized system to pass the information to the central records office.
2005 is the year it was introduced so its marginal as to whether they have all the information you are after but you might be able to get a couple of years worth of info.
Nothing can be obtained using just the vehicle registration number though you have to get the MOT number.
All the best