Any question answered...

@nick_h.

If they actually had a warrant, it looks like they will need a new one as they had 28 days.

Page 245/246
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/490992/Electricity_Act_1989__Energy_Bill_2015-16_Keeling_Schedule_.pdf

Non-payment of suppliers' charges
2(1) Where a customer has not, within the requisite period, [made all the relevant payments], the supplier
may--
(a) install a pre-payment meter on the premises; or
(b) disconnect the premises,

(2) The power of a supplier under sub-paragraph (1)(a) or (b) may not be exercised--
(a) as respects any amount which is genuinely in dispute
.

If your sure you don't owe them (or the previous supplier that they took over) and your disputing it, they shouldn't be trying to install a payment meter.

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