Yes. If your contract with the lessor is for a Citroen Picasso and instead you are stuck with a small courtesy car for an extended period then you are entitled to the difference in the lease payment between your Picasso and the small courtesy car. Make that very plain to the leasing company. It may be covered by section 75 of the Consumer Credit Act 1974 or by basic contract law that puts the lessor in beach of contract to the lessee: www.honestjohn.co.uk/faq/consumer-rights/