The discount mechanics are operator-specific. Sykes, Holidaycottages.co.uk and Cottages.com all run dedicated last-minute pages that surface short-notice availability — typically with a 10-25% reduction on the listed weekly rate, sometimes with a free-night promotion (book 7 nights pay 6 in the truly soft weeks). Hoseasons and Park Holidays UK operate at the caravan-park end with similar mechanics. The smaller agencies (Toms Holidays, Cornwall Hideaways) are less discount-driven; their model is curated and they hold pricing better.
The best windows for genuine value: late January through early March (post-Christmas, pre-Easter); the second and third weeks of November (between half-term and Christmas); late September into October half-term (the warmest sea, often empty cottages); and the awkward week between Easter and the May bank holiday. Peak summer (mid-July through August) sees almost no last-minute discount — supply is committed and any property still available at short notice is either premium-priced or has a reason not to be booked.