To support charitable work and youth mobility, the Home Office allows for non-EU nationals to come to the UK to do voluntary work, but there are strict conditions about what you can and cannot do.
If you meet the following requirements, you can come to the UK as a voluntary worker:
You can stay in the United Kingdom for a maximum of 12 months as a voluntary worker. There is no limit on the number of times you can come to the UK as a voluntary worker, but you must not plan to live permanently in the UK.
You must do fieldwork offering direct assistance to those the charity is there to help, for example, elderly, disabled, vulnerable or homeless people.
You should not be employed by the charity or hold a job which a resident worker would normally be paid to do.
You must not receive pay for the work you do, though you may receive reasonable expenses. Some voluntary workers may receive subsistence payments.
People who enter the UK in other immigration categories (including visa nationals) can apply to stay as voluntary workers if they meet all the immigration regulations.
You can apply to extend your stay as a voluntary worker, but only up to a maximum total stay of 12 months.
If you are a visa national you will have to apply for entry clearance before coming to the UK.