Payroll giving lets you donate a regular amount directly from your salary through your employer's payroll. The donation is given before tax (but after National Insurance) is taken off, so the charity automatically gets more, regardless of what level of tax you pay.
If you're a basic-rate taxpayer, you pay 80p for every £1 donation. For higher-rate taxpayers, it's 60p, and for additional-rate taxpayers, it's 55p. In other words, the charity gets the tax that you would have paid, on top of what you're actually paying, ie, the full £1.
The only problem is employers must have a scheme in place: you can't just do it on your own. Ask your HR department if your firm runs a scheme. If not, it's worth trying to encourage it. It's a simple process run through automated payroll systems. The
Association of Payroll Giving Organisations (APGO) may be able to help.
Unfortunately, self-employed sole traders can't access payroll giving.