iPhone SE in Black (Refurbished) with 64Gb storage with Unlimited data, calls and texts for £22.99 a month with no up-front fee.
(Other colours are out of stock)
ID Mobile use the Three Network, so should be near identical coverage and data speeds. Voice Over LTE and WiFi Calling is also offered by ID Mobile too.
If you do want less data they have 5GB for £19.99 a month or 20GB for £20.99 a month.