According to the 1989 lighting regulations, you can have as many additional main beam lights as you like (the two standard ones meet the requirements for mandatory lights.) They can be anywhere you like on the vehicle (including the roof) and you can have any number including odd numbers.
The only requirements for any you do fit is colour (white or yellow) that they are wired to only come on with main beam (with an isolator switch to turn them off entirely if you want) and that they face forward. On a 1991 or newer vehicle, they also have to be E-marked. There's nothing I've found in the regulations specifically saying that 55w is a maximum as is commonly assumed.
https://www.landyzone.co.uk/land-rover/adding-extra-lights-the-legislation.290172/