I assume that you'll be eligible for free UK health care.
First, register with a local doctor (general practicioner/GP).
www.nhsdirect.nhs.uk is a place to start to find one.
Tell the doctor that you are on a pump. They will need to refer you to a hospital with a pump trained team. (I think that there is one in High Wycombe, there may be one closer to Reading). Pumps are not terribly common in the UK, but there are a reasonable minority on one.
The way it works (I am on a pump) is that I see the hospital doctor twice a year for a diabetes check up. My GP prescribes (issues) my insulin to go into the pump & my blood testing strips for my meter, as directed by the specialist diabetes doctor. The cartidges/reservoirs, infusuion sets & cannulas are ordered for me by the hospital and delivered directly to me at home by the pump manufacturer every three months.
If you are not eligible for free UK NHS treatment, the best thing to do is go to see a GP as soon as possible (you shouldn't have to pay for this if you are an EU national and you have an E111 card) and ask them to refer you to a private doctor who can prescribe your pump supplies. I expect that the way the supplies arrive to your home will be the same, just the mechanism for getting the order done will be different.
It is a good plan to pile up the supplies before you come, getting an appointment with a specialist on the NHS can be quite slow as it is publicly funded.
You will not have any trouble getting insulin & test strips from a GP in the UK, even if you have to pay for the prescription. If the worst happens and you have to buy your own pump supplies, you can order them from the manufacturer by phone and pay by credit card.
The most common pumps in the UK are the Accu Chek Spirit Combo, Medtronic Veo, Animas 2020 or Vibe & Omnipod. All have UK helplines. It may be that a call to your German helpline for your pump manufacturer will advise you how you can get interim supplies while you settle into the UK system.
I hope that this helps.