Who tracks council by-election results in the UK?: Mark Pack runs the most-followed council by-election tracker at markpack.org.uk, monitoring ward contests to identify national trends before they show in polls.Source: uk-elections-2026
What does markpack.org.uk track?: It tracks UK council by-election results, aggregating ward-level data to identify trends for parties like Reform UK, the Greens, and Lib Dems.Source: uk-elections-2026
How many Reform UK councillors have quit since 2025?: 65 of the 677 Reform UK councillors elected in 2025 had quit, defected, or been expelled by April 2026, per HuffPost UK data.Source: uk-elections-2026

Background

Mark Pack is a Liberal Democrat activist, writer, and former party co-chair who runs the UK's most-followed council by-election tracker at markpack.org.uk. His data was cited in reporting on Reform UK's internal collapse after 65 of 677 Reform councillors elected in 2025 quit, defected, or were expelled within a year , underscoring the value of granular local-election monitoring that Pack pioneered.

Pack has built a reputation as the go-to source for sub-national election data in British politics, filling a gap Left by mainstream polling. His tracker aggregates results from hundreds of ward contests each year, making it possible to spot national trends — such as Reform attrition or Green gains — before they register in Westminster polls. He was elevated to the House of Lords in 2022 as Lord Pack of Masson, making him one of the few prominent Lib Dem data analysts to sit in the upper chamber.

In the 2026 local election cycle, Pack's work feeds directly into the emerging narrative of council politics as a leading indicator for general elections. His tracker data on departing Reform councillors was specifically cited during the post-7 May attrition discussion.