How postwar Royal Navy type numbers divided missions

When did the Royal Navy begin using numbered type designations such as the Type 4 family?

The system developed after the Second World War as frigate and destroyer roles were reorganised into mission-based number families.

The system dates to the postwar reorganisation in which destroyers were converted and new frigate categories emerged. Type 2 numbers identified anti-submarine frigates and Type 3 numbers identified general-purpose frigates. Type 4 numbers denoted destroyers, while Type 8 covered very large destroyers that could amount to cruisers in all but name. The scheme organised the Royal Navy's changing surface fleet by mission families as well as size.