OnePlus is a Chinese company that was founded in 2013 and serves thirty-eight countries and regions worldwide including the UK. They primarily focuses their manufacturing efforts on cellphones, but create and sell other products as well.
 
So far, the OnePlus company has produced eight different phones.
 
Their original phone, the OnePlus One, came out in 2014 and ended up being quite popular thanks to its affordability as well as its better specifications when compared to other phones that were released that year. Ultimately, the OnePlus One was highly successful

Their next phone, the OnePlus Two came out a year after the One (in 2015) and also turned out to be quite popular; it was also one of the first smart-phones at the time to switch from using an ordinary micro USB port to a USB Type C port instead.
 
Their third phone was the OnePlus X, which was released a few months after the OnePlus Two. This phone was the company’s first entry into the “budget phone” market, meaning that it is cheaper when compared to fancier smart-phones; additionally, the X from OnePlus is smaller than the One and Two phones (at 5 inches rather than 5.5”) and featured more or less the same construction as the OnePlus One but with an AMOLED display instead.
 
OnePlus's next phone, the OnePlus 3, debuted in June of 2016 and achieved tremendous popularity for offering both excellent specifications and an affordable price. The OnePlus 3 is in fact still in use today because of its high quality design; while finding a brand new OnePlus 3 is likely going to be difficult due to the fact that OnePlus has since moved on to manufacture newer phone models, there are still quite a few shops and online stores (such as Handtec) that sell refurbished OnePlus phones like the OnePlus 3. And not only will these refurbished phones be cheaper, they will come unlocked, Sim-free, and ready to use; you won’t need to worry about signing up for any sort of long-term phone contract.

Here in the UK you can take out a sim only contract from as little as £5 a month offering free minutes and internet
 
After the 3, OnePlus went on to manufacture the 3T, which was essentially a slightly upgraded version of the original OnePlus 3. This newer version of the 3 features a higher capacity battery as well as additional storage space (with the option to choose either 64GB or 128GB of storage).
 
OnePlus’s next phone was the OnePlus 5 just recently in 2017. In addition to a dual-lens camera set-up, it has 8GB RAM and up to 128GB of storage for your media and messages. It also comes in two available colours, Midnight Black and Slate Grey (there have also been two limited edition colours in the past; while the company is no longer producing these limited edition versions of of the OnePlus 5, it’s possible you could purchase a refurbished OnePlus from Handtec UK).
 
OnePlus also released the OnePlus 5T, which (like the 3T to the 3) is an upgraded version of their previous phone. The 5T features a facial recognition program for unlocking the phone, as well as an improved dual-lens camera.
 
Finally, the most recent phone produced by OnePlus is the OnePlus 6, which became available for purchase in spring of 2018. This phone is notable for its all-glass water-resistant design, which sets it apart from other smart-phones currently on the market. This phone is also the first phone created by OnePlus to offer a variety with 256GB of inbuilt storage.

See link below for the latest refurbished Oneplus units from Handtec