Butler was killed by a luggage lift at Burghley House while attempting to free an item of baggage.
Serco has previously left staff with no wages and failed to pay contractors.
Latest news, sport, weather and travel updates from across Lincolnshire on Monday 27 February
Sunday Politics Yorkshire and Lincolnshire looks back at the week's political headlines.
BBC Sport looks at how Lincoln City celebrated
FA Cup quarter-finalists Lincoln maintained their three-point National League lead by beating bottom club North Ferriby.
About these results
As BBC Radio 5 live
What do they do inside the House of Lords?