Mark Pack

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.

Pack's council by-election and councillor-attrition tracker recorded Reform UK's cumulative councillor departures reaching roughly 40 by 2 July 2026, a sharp slowdown from the 22 lost in the fortnight after the May local elections. A separate tracker cites nearly 100 departures across the 2025 and 2026 cycles combined, a different measurement period that should not be blended with Pack's own figure.