There are many issues an organisation needs to think through if you're thinking about raising funds by selling alcohol at an event.
Members of some communities and faith groups don't drink alcohol, and may not want to be in places where alcohol is being consumed. People with drink problems may also want to avoid events where alcohol is available. So, while you might raise money, you might also put off some people - the balance will vary from organisation to organisation.
As regards the law, the Charity Commission has produced guidance for registered charities. You can sell alcohol as refreshments at an event or activity your charity is running that is directly connected to the charity’s aims, such as amateur sports fixtures or theatre performances. As long as you stick to the rules (see the Charity Commission guidance), you shouldn't have to pay tax on the sales.
You should consider the risk of financial problems for your group, for example if you buy more alcohol than you sell. And you should also consider any potential risks to your group's reputation.
You'll also need a licence from Redbridge Council, and to check that your organisation's governing document doesn't forbid the selling of alcohol, and that the rules of the building you're planning to use don't either.
Your charity can give alcohol away at events or meetings without a licence, but you must make it clear that the value of the alcohol is not included in any ticket price or entrance fee - so you can't avoid the need for a licence by saying, for example, that the entrance price includes a free alcoholic drink.