If you speak a foreign language, preferably an Asian or African language; or if you know BSL, you might be able to switch out of a visitor visa into a volunteer visa and extend your stay by up to 1 year. Various registered charities in the UK are almost always in need of translators.
In addition to translators, there are volunteer opportunities for other skill sets like rehab, elderly, various sorts of carers, drivers and so on.
That's the good news. The bad news is that volunteer visas are fiercely contested for by all sorts of non-visa nationals (mostly *other* boyfriends/girlfriends who want to do the same thing), and the competition is indeed keen. Also, the in-country switch from visitor to volunteer doesn't work for visa nationals, because visa nationals need an entry clearance specifically designated as volunteer.
A volunteer visa works something like a work permit, a registered charity sponsors the applicant for a specific role over a specific interval of time. Let's have a look at the rules:
However, the Home Office has allowed a concession to allow people from outside the EEA to volunteer if they meet the following criteria:- the activity is purely voluntary and does not involve taking up a salaried post or permanent position of any kind within the charitable organisation or entering into any arrangement that is likely to constitute a contract of employment; and
- the activity is either for a charitable organisation listed in Home Office guidance or a registered charity whose work meets the criteria set out in this instruction; and
- the activity is unpaid, or is not likely to be subject to payment of the National Minimum Wage [see our information sheet on the National Minimum Wage] and directed towards a worthy cause; and
- it is closely related to the aims of the organisation; and
- it is fieldwork involving direct assistance to those the charitable organisation has been established to help; and
- the passenger intends to leave the United Kingdom at the end of their stay.
So if you think it might work for you, then you would approach registered charities in your area and present your credentials. Not every need is posted on their web sites, and they can be opportunistic if they think you have an interesting skill to offer - they are not subject to the full rigour of establishing non-fulfillment from within the EU.
As a final note, I would add that you need to plan it out before the 11th hour because it takes some time to set up the arrangement, and trying to switch in the 11th hour will raise question marks. Needless to say, trying to switch into a volunteer visa from an overstayer status is a waste of everyone's time. Planning ahead pays off...
