(11 Nov 2023, 9:12 pm)Jimmi wrote Think it would've been the 213 back then, became the 21 in 2008 as part of the overhaul of services in the Peterlee area whilst the 214 to Middlesbrough became the 21A (Sunderland - Peterlee leg became 31/31A to avoid the use of Tachos at some later stage). It was curtailed in Peterlee in either 2011/12 but was extended to Sunderland again as the X21 in autumn 2014 before becoming the X21 for the whole route shortly after. It stopped serving Sunderland again in October 2019.
Interesting detailed history. With a few interurban routes I am more likely to remember the specific journey but not necessarily the route number.