Interest charge for RTB receipts retained with GLA

Our housing department have transferred RTB receipts to GLA and at the time they thought it can be drawn as and when required without any time restrictions. However, they found out recently that RTB retained with GLA needs to be spend within 3 years of transfer. We informed GLA that If this is the case, then there is no benefits as Council can keep the fund for 3 years under current RTB legislation. 

GLA told us that Council keep RTB fund up to 3 year and just before  3 year expires transferring it to GLA, effectively giving Council 6 years to spend RTB receipts. 

However, as per RTB 1-1 agreement if fund are returned after due date, interest is chargeable.

That means in order to get 3 years extension, Council is required to pay interest.

In summary, there is no benefit in transferring future fund to GLA.

I would like to know how other Council are dealing with retained RTB?

Thank you.