Can he enter using his existing Visitor visa, ... It’s possible he may be invited to the UK as a performer for one month ... Can he enter using his existing Visitor visa, provided he has a written invitation from the UK-based organisation...
Based on your given source your partner, when invited, can engage in such an activity during the first month and then remain a further 5 months.
You can visit the UK for certain paid engagements or events (a ‘permitted paid engagement’) if you:
- have a written invitation from a UK-based organisation or client for a pre-arranged event or other permitted engagement
- can show you’re an expert in your profession
- are 18 or over
The engagement must be relevant to your expertise, qualifications and main job in your home country.
You can come to the UK for up to 6 months, but you must do the engagement in the first month.
would the sponsor need to inform UKVI?
Since the page mentions only a written invitation (and not a certificate of sponsorship), it sounds more like a letter that should be presented at the port of entry.
Your invitation
You must have an invitation from a UK-based:
- creative organisation, such as a gallery, university arts faculty, school or events venue
- agent or agency
- broadcaster
For working as a performer longer than 1 month the answer would be no for someone who normally requires a visa to enter the United Kingdom:
Overview
You must apply for a Temporary Work - Creative Worker visa if:
A creative worker is someone who works in the creative industries, for example an actor, dancer, musician or film crew member.
This visa has replaced the Temporary Worker - Creative and Sporting visa (T5). If you’re a sportsperson, you can work in the UK with the International Sportsperson visa.
Sponsorship
You need to have a certificate of sponsorship from a licensed sponsor before you can apply to come to the UK to work.
The work you do in the UK must relate to the work of your sponsor organisation.
For those who do not normally require a visa to enter the United Kingdom:
Information for entertainers and musicians, from non-visa national countries, such as EU Member States and the US, visiting the UK for performance and work.
What you need to know
The UK does not have work permits. The UK’s domestic rules allow musicians, entertainers and artists from non-visa national countries, such as EU Member States and the US, to come to undertake paid work in the UK for up to:
When you arrive in the UK
You must see an immigration officer when you arrive in the UK - do not use the automatic ePassport gates. The officer will:
- check your certificate of sponsorship is valid
- check you have enough money to support yourself - check how much in the eligibility requirements
- stamp your passport
You will not be allowed to work if you use an automatic ePassport gate. You must see an immigration officer and get a stamp in your passport.
- 6 months without requiring a visa if performing at a permit-free festival. The list of permit free festivals is published under the Immigration Rules and includes a range of events, from Glastonbury to Glyndebourne.
- 12 months on the Temporary Work - Creative Worker [see above] route, if they obtain a visa and a Certificate of Sponsorship.
Sources:
Appendix V: Visitor
Additional eligibility requirement for Visitors coming to the UK for Permitted Paid Engagements
V 13.1. Where the applicant is seeking to come to the UK to undertake a permitted paid engagement, they must be aged 18 or over when they enter the UK.
V 13.2. The applicant must intend to do one (or more) of the permitted paid engagements set out in V 13.3. which must be:
(a) arranged before the applicant travels to the UK; and
(b) declared as part of the application for entry clearance or permission to enter the UK; and
(c) evidenced by a formal invitation, as required by V 13.3; and
(d) relate to the applicant’s area of expertise and occupation overseas.
V 13.3. The following are permitted paid engagements:
...
(e) a professional artist, entertainer, or musician coming to carry out an activity directly relating to their profession, where they have been invited by a creative (arts or entertainment) organisation, agent or broadcaster based in the UK; and
...
Appendix Visitor: Permitted Activities - Guidance - GOV.UK
...
Creative
PA 14.1. An artist, entertainer, or musician may:
(a) give performances as an individual or as part of a group; and
(b) take part in competitions or auditions; and
(c) make personal appearances and take part in promotional activities; and
(d) take part in one or more cultural events or festivals on the list of permit free festivals in Appendix Visitor: Permit Free Festival List.
PA 14.2. Personal or technical staff or members of the production team of an artist, entertainer or musician may support the activities in PA 14.1. or Appendix V: Visitor at V13.3 (e) provided they are attending the same event as the artist, entertainer or musician, and are employed to work for them outside of the UK.
PA.14.3. Film crew (actor, producer, director or technician) employed by an overseas company may visit the UK to take part in a location shoot for a film or programme or other media content that is produced and financed overseas.
...
Permitted Paid Engagements
PA 19. A Visitor may undertake the permitted paid engagements in V 13.3, providing they are completed within 30 days of the Visitor’s entry to the UK, and the requirements of V 13.1. to V 13.2. are met.
