If you are an employee 'Give as You Earn' is the most tax efficient way to make regular donations.
Under the scheme, you make a donation tax-free from your gross salary to any cause of your choice. This means that if you're a basic-rate taxpayer pledging say £10 a month, it will only cost you £7.80.
For most people, the easiest way to join the Give As You Earn scheme is to do so directly through their employer. You would need to give The Prior Foundation as your charity of choice quoting charity number 281242.