If you want an iPhone but cant afford a new one, youll need to do some creative shopping. eBay has a couple of options for you note that these are used or seller refurbished units.
A used iPhone 7 (Grade A) starts at £۳۲۰, which goes up to £۳۷۵ for 128GB and and £۴۰۰ for 256GB. Certain color/storage combinations are out of stock and the Red color option is usually a bit pricier. You can find the deal here, delivery is free and theres a 12 month warranty.
Then theres a seller refurbished iPhone SE. The cheapest unlocked model is £۱۳۵ (۱۶GB, Good condition) and prices start climbing up quickly if you want a better-preserved phone Pristine condition is £۲۱۰! You also get 12 month warranty. Here is the deal, shipping to the UK is free.