All I've found is this ...
Exchange Policy
Subject to the following terms and conditions, any vehicle purchased from a Lexus Centre ('the Centre') with Lexus Pre-Owned status ('the Vehicle') may be exchanged for another vehicle ('the Replacement Vehicle') at the same Centre, providing that:
the Centre is satisfied that the Customer is a private purchaser (and not a trade purchaser or otherwise).
the Centre is satisfied that, with the exception of fair wear and tear, the Vehicle is in the same condition as at the time of delivery to the Customer.
the Vehicle is returned to the supplying Centre within 30 days of the delivery date.
the Vehicle has covered no more than 1,000 miles since delivery to the Customer.
the Centre is satisfied that the Customer owns the Vehicle and is fully entitled to exchange it under the Agreement.
The Customer may choose any vehicle as the replacement vehicle, provided that:
it is readily available at the same Centre, and
it is of an equal or higher value than the original invoice price of the Vehicle.
Before any exchange is effected under the Agreement, the Customer shall be responsible for making all the necessary arrangements relating to terminating, transferring, or taking out or otherwise dealing with the financing arrangements for the purchase of the original Vehicle and the Replacement Vehicle. Any exchange shall be subject to the Centre being satisfied with such arrangements. In particular if the original Vehicle is subject to a Hire Purchase Agreement, a new agreement must be completed and the relevant deposits paid by the Customer.
Where the Customer has chosen a Replacement Vehicle with a higher price, the price difference must be paid to the Centre before the exchange takes place.
The Customer will be responsible for any additional costs resulting from the exchange such as transferring insurance or personalised number plates.
This Agreement only applies to the Vehicle purchased. Only one exchange will be considered and this Agreement shall not apply to any Replacement Vehicle.
This Agreement does not affect any of the Customer's statutory rights.
https://www.johnsonscars.co.uk/lexus/used-offers/approved-used-programme/