The dual registration measure is for operators working on a ‘hire or reward’ basis who have an established haulage base outside Great Britain (GB) and who also maintain a GB haulage base.
Dual registration allows operators to temporarily transfer their vehicles between their 2 operator’s licences. This means a GB-registered or EU-registered vehicle will be subject to the market access rules of the country where their haulage bases are registered, provided the vehicle(s) have been transferred onto the relevant operator’s licence.

In brief, under dual registration, if GB-registered vehicles are transferred onto an operator’s licence registered to an EU base, EU internal market rules apply to those vehicles. If EU-registered vehicles are transferred onto an operator’s licence registered to a GB base, GB domestic rules apply.   
Without dual registration, a GB-registered vehicle entering the EU on a GB operator’s licence would have their movements restricted by the EU’s rules applying to international goods vehicles.
Similarly, EU-registered vehicles entering the UK on an EU operator’s licence would have their movements restricted by the GB rules applying to international goods vehicles.
The vehicles will need to be registered and comply with domestic legislation in the countries in which their bases are established.

Hauliers using this measure will be exempt from paying Vehicle Excise Duty (VED) on a foreign-registered vehicle whilst the vehicle is temporarily operating on a GB operator’s licence.
The VED exemption only applies to vehicles brought into GB temporarily. The department interprets ‘temporarily’ in most cases as being no more than 6 months in any 12-month period. This period aligns with the rules on temporary imports. This can be a single visit, or several shorter visits. There is no minimum time period between exit and re-entry.
Operators are required to specify (register) the vehicle(s) prior to its first use under their GB operator’s licence, and to remove the vehicle from their GB operator’s licence when it leaves GB. This is to ensure that the vehicle(s) do not inadvertently exceed the 6-month limit. This can be done by contacting the Office of the Traffic Commissioner at tcco@otc.gov.uk.
To add the vehicle back on to their international operator’s licence, operators will need to contact the relevant competent authority where the international base is established.

There is specific criteria and eligibility to use the dual registration:

Eligibility and criteria
The criteria an operator must meet to use the dual registration and VED exemption are that:
•    the operation consists of national carriage for hire or reward by a haulier who is a holder of a Community Licence or an authorisation issued by the relevant authority in the country of establishment - if the driver is not a national of an EU member state, they must hold a driver attestation relevant to the territory in which the haulage base is established
•    the vehicle has been specifically designed or substantially modified to carry the goods set out below
•    the goods being carried are property, equipment or animals being carried to or from theatrical, musical, film or circus performances or sporting events, exhibitions or fairs, or to or from the making of radio or television broadcasts or films
•    the goods being carried are loaded, unloaded or reloaded within GB - the goods must remain unchanged

Operator licences
To function as a haulage operator, the haulage company will need an operator’s licence (sometimes called an O licence) which must be held by the person – whether an individual, partnership or a company – who ‘uses’ the vehicle and this may or may not be the owner of the vehicle.   

The operator will be responsible for ensuring that all operator licensing and road safety requirements are met, including complying with drivers’ hours and tachograph rules and maintenance commitments, ensuring that vehicles and trailers are roadworthy to UK standards prior to use in the UK. Foreign-registered vehicles are subject to the same rules as vehicles registered in the UK.

Transport manager(s) must be appointed and must be of good repute and have a Transport Manager Certificate of Professional Competence (CPC).  The appointed person must be resident in the EU for the EU O-licence and resident in the UK for the GB O-licence.

You are advised to read the guidance from DVSA

Further information:
https://www.gov.uk/guidance/dual-registration-for-specialist-events-hauliers?utm_medium=email&utm_campaign=govuk-notifications-topic&utm_source=a32acd80-b9a7-4052-924d-c06866041d3c&utm_content=immediately