We have heard about a Lithuanian company called Think Container who can supply shipping container garden offices to the UK. If you are looking for an industrial looking office, they could be a good option.
The containers come in several configurations from a single container through to models where they are stacked one upon the other. The basic container size is 6050mm x 2430mm x 2820mm high. Because of the height of the container, you would need to site it at least 2 meters from any boundary for it to fall under Permitted Development rules. Otherwise, you would need to apply for Planning Permission to install it.
The containers are insulated with 100 rock wool insulation and have a 10mm internal chipboard finish, which is a bit more basic than the UK designed garden offices. You have a choice of finishes from the outside from a white plastic to a coloured steel and timber finish.
The starting price for the single container unit with glazed front elevation ifs 6050EUR plus delivery to the UK, the higher spec version with steel and timber exterior starts at 9438EUR plus delivery, so these containers are not a cheap option!