It comes as the Petrol Retailers Association warns that up to two-thirds of its members are out of fuel.
The changes - opposed by many on the left - give MPs more say in choosing future Labour leaders.
A 36-year-old was arrested on Sunday in what police describe as a "significant development".
The vote comes after leader Sir Keir Starmer rules out putting big energy firms into common ownership.
Lead singer Francis Rossi calls Lancaster an integral part of the band's sound and success.