Removal notice from an enforcement agent for council tax, can they get in while I'm out?

No

Bailiffs may not enter a dwellinghouse using reasonable force, because this power is expressly reserved for entering commercial premises,^[1] recovering unpaid tax owed to HMRC,^[2] or unpaid court fines.^[3]

If you leave a door unlocked while you are out, the bailiff may enter by opening the door.^[4]

If you leave a key in the lock of a locked door, the bailiff may enter by turning the key.^[5]

The use of a landlord's key to gain entry is unlawful.^[6]

If the key is found but is not in the lock, entry would be unlawful.^[7]

A bailiff cannot put his hand in a hole (e.g. a cat flap or letterbox) in order to pull back a bar or fastening to open the door or window because this amounts to burglary and trespass.^[5]

Enforcement agents must only use a door or usual means of entry to enter premises.^[8]

^{[1] Paragraph 18A(1)(b) of Schedule 12 of the Tribunals, Courts and Enforcement Act 2007
[2] Paragraph 19(1)(B) of Schedule 12 of the Tribunals, Courts and Enforcement Act 2007
[3] Paragraph 18(b) of Schedule 12 of the Tribunals, Courts and Enforcement Act 2007
[4] Regulation 20 of the Taking Control of Goods Regulations 2013
[5] Ryan v Shilcock [1851] 7 Exch 72
[6] Miller v Curry [1893]
[7] Welch v Krakovsky [1919]
[8] Paragraph 59 of the Taking Control of Goods: National Standards 2014, April 2014}