Absolutely not, this is a violation of the terms of visiting as a visitor (tourist). In order to do charity work or volunteering, you must apply for a special visa, Tier 5 (Temporary worker - Charity Worker). You must be sponsored by a licensed employer and have a certificate of sponsorship to apply. 1 A visitor also cannot do any work, even online, paid babysitting or studying while in the UK.

• 1. https://www.gov.uk/tier-5-
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