When you need planning permission for a UK extension in 2026, Permitted Development size limits, neighbour consultation, Article 4 areas, costs and timelines. This guide is written by PG Property Repairs and Renovations, an FMB and TrustMark accredited building company based in Worthing, using real costs and timescales from projects completed across Worthing, Lancing, Shoreham, Brighton and the wider West Sussex area.