Holders of Merlin Annual Passes are now able to bring friends and family to Chessington World of Adventures and Thorpe Park for £10 each.
Lasting until 8 September, the offer also includes a discounted rate of admission of £7.50 at Warwick Castle.
The move is widely expected to be part of Merlin’s attempts at boosting visitor numbers this year ahead of the company listing on the London Stock Exchange following the end of this season.
The new offer requires the pass holder to telephone a booking line at least 24 hours in advance of their visit, in line with the usual friends and family offer.