Here's a very brief list of points of importance. The critical question is: do you hold a driving licence which is valid in Great Britain?
In order to lawfully drive a motor vehicle on a public road in England, Scotland or Wales (i.e. Great Britain), you will need:
- A driving licence that is valid in Great Britain.
- Motor vehicle insurance valid in Great Britain.
- An entry visa valid for Great Britain.
If you have passed your driving test in a country outside both the UK and the countries of the European Economic Area (EEA), you can only drive any small vehicle (e.g. a car or motorcycle) which is listed on a full and valid driving licence issued to you by your own government (i.e. only a type of vehicle you are allowed to drive in your own country), but NO vehicle if you only possess a provisional licence instead of a full one, and only for a period not exceeding 12 months from the date you entered Great Britain.
Bear in mind that if your driving licence is only valid for a vehicle with automatic transmission, you will only be able to hire that type of car. Don't make the mistake of hiring a car with a manual gearbox in that situation (quite a common mistake, seemingly).
If you fly into an airport in the UK, and hire a car there, the car hire firm will help you arrange UK motor vehicle insurance (and should normally lease you a car already fully taxed and MOT'd). But any such insurance will be invalid if you do not possess a full, valid driving licence for the vehicle hired to you - something which would render you liable to arrest and prosecution.
It is essential to bring with you, into the UK, your full driving licence issued to you by the government in your country of origin. You will need it to hire a car here. If it is not in English, even if it is valid you might still encounter difficulties (in the event of a road accident a UK policeman will probably not be able to read it), so a translation of it could be helpful.
The UK's Highway Code merely sets out the rules of the road. It tells you in what circumstances you will be liable to criminal penalties, and for financial loss caused to other road users in civil law (i.e. if you have an accident because you have not complied with the rules in the Highway Code).
There are quite a lot of circumstances in which a driver can incur criminal prosecution without having an accident. For example, driving on the wrong side of the road (something any policeman would certainly notice).
Motor insurance is a compulsory legal requirement, and its intention is to meet any civil claim made against you in court by another road user, so will normally only need to be claimed on by you in the event of your having a road traffic accident / collision.
The Highway Code is only part of the story: road signs on the highway verge are very common in the UK, especially speed limit signs. Bear in mind that these are all in miles per hour, and that most distances will be posted in yards or miles.