its the 50% of the security deposit the RAC keep when you return the Carnet upon return home, lots more info in the link I posted above.
Below is a quote from a adventurebikerider.com thread on the same subject
"The RAC, up until sometime in 2012/13 had in place a system whereby the cost was made up of a document payment, an administration fee and thirdly a deposit. It is the deposit that is the problem and this fee can be colossal.
The deposit is based on a multiplier of the value of your vehicle and ranges from 1.5x e.g. for Australia, all the way to 8x for Egypt (for an £8,000 motorcycle it is £64,000). The excessive cost is to cover the huge fees and costs levied by a country, should the vehicle be left, illegally, on their soil. For this reason most travelling vehicles are old, using a newish vehicle being reserved for the rich.
Previously a UK resident could either:
1) pay the full deposit up to a maximum of £10,000 direct to the RAC and get it back on return to the UK, or
2) arrange a bank guarantee to ring-fence/freeze funds in the applicants bank to cover the deposit to the benefit of the RAC should a claim be made by a foreign country, or
3) Pay a fee of 10% of the deposit to an insurance company (one had to fill in a application form to the company and process it through the RAC). 50% of this cost being refunded upon the vehicles return.
In this last item, the insurance company was a specific one designated by the RAC . It was also the one taken by people who did not have sufficient funds to supply a deposit or a bank guarantee.
Now however, the RAC have removed the deposit and bank guarantee and will only allow the 'insurance' that they now call a security. It is also now 10.6% of which, 50% of that (i.e. 5.3%) is refunded on vehicle return.
Going back to our £8,000 motorcycle through Egypt, this, on top of fees, would cost almost £3,400. A fee that previously could have been circumvented.!"