I am not well-versed in UK tax matters, but quick googling seems to indicate that recipients do not pay tax on received gifts, although the givers may have to pay tax on amounts that they gift others, above a threshold [looks to be 3k in most cases]. If this isn't a gift, then it seems to be personal income earned by you in a non-incorporated business, and thus could be taxable.
HOWEVER - be cautious about claiming that the money you are receiving is a 'gift'. You state that there is no benefit given to these people and that you 'do not know why they do it', yet very clearly there is public recognition of the gift in a way that indicates they may have motives to do so. From what you have said, these people are expecting their names to pop up on a leaderboard by giving you money.
You could argue that someone buying a 'lootbox' in a videogame receives "nothing tangible but bragging rights indicated by the cosmetics that they then win", yet gaming companies don't report these amounts received as 'gifts', they record them as taxable revenue.
There is a question, then, as to whether HMRC will agree with the idea that this is a gift, or is in fact business income you earned by clever social marketing. UK Tax law is largely based on legal precedent from prior cases that have made their way through the courts. In order to get guidance on what the current interpretation for your situation would be, you would need to hire a competent UK tax practitioner.
If the amount you are earning through this is too small to seem 'worth it' to contact a tax accountant / lawyer, I highly recommend you just claim it as income to be safe, and pay tax on it. If it would be a large amount of tax (into the multi-thousand pounds territory), consider paying for legal advice to guide you on whether you would have justification to claim these as non-taxable gifts.