Solent controllers have the un-enviable task of controlling IFR commercial traffic within the class D segment (especially N, N/E of Southampton airport) and approving GA crossing clearances at the same time.
As Standard Noise said, he/she may have been trying to coordinate your requested clearance with a fellow ATCO.
Another problem that often arises is a protracted exchange of RT calls for a crossing clearance just as commercial traffic is being vectored for approach. Failing to further clear the commercial traffic down the approach (especially in the vertical sense around SOU) due to other RT exchanges can result in traffic being left high (thereby delaying proceedings due to extra track miles) or (worst case) a go around and re-vector.
If you're asked to remain OCAS or standby, it may well be due to this and the need to balance / prioritise the controller workload.