I was going to reply in the negative until I read Joe’s post. A quick look at the ‘Flexed’ website does not make it clear whether the cars are new or not, how much delivery charges would be, or if rentals are fixed at monthly periods. Insurance is extra and likely very high. Five weeks, as per your lease in Germany, is not considered long term.
It looks like the Citroën and Peugeot short term rentals are no longer available in the UK since it left the EU. I’d stick with Autoeurope. I’ve used them a number times, a Europcar vehicle, and my rental cars have all been almost new. I take out what is called Super Cover (covers tires, windshield etc): it’s expensive, but does give you a peace of mind. Note, you’ll notice that rentals in the UK are a bit pricier than on the mainland.
PS: Tina, you have started two almost identical threads.