The British Standard requires that we ask for evidence for any employment gap period of more than 31 days. This could be when you were unemployed, studying, on sabbatical, travelling or on holiday for example.

Paragraph 3 of section 7 of the standard says this:

For screening purposes, the organization should establish by direct reference to current and former employers, government departments, educational authorities, etc., with confirmation from them in writing, the details of education, employment, periods of self‑employment and unemployment of the individual being screened for the whole of the screening period (see 7.6) with no unverified periods greater than 31 days.