All prices quoted in advertisements must include VAT, unless it is clear from the advertisement that these prices are available only to those who pay no VAT or can recover VAT (e.g. VAT registered businesses). If this is the case, and the ad makes clear that the price quoted is available only to business/trade customers, the copy must make clear that prices are “exclusive of VAT” and state the rate of VAT. “Trade price £50 plus VAT at 20%”.
Advertisers who offer a VAT-based price reductions to consumers (but still pay the VAT to the Treasury themselves) may state that their products/services are “VAT-free”.