Group 3(\+44\s?\d{4}|\(?0\d{4}\)?) 1st Alternative\+44\s?\d{4} \+the literal + (4310 / 538 / 2B16)
\s?optionally matches any whitespace character
\d{4}a digit, repeated exactly 4 times
2nd Alternative\(?0\d{4}\)? \(?optionally matches the literal ( (4010 / 508 / 2816)
0the literal 0 (4810 / 608 / 3016)
\d{4}a digit, repeated exactly 4 times
\)?optionally matches the literal ) (4110 / 518 / 2916)
\s?optionally matches any whitespace character
\d{3}a digit, repeated exactly 3 times
\s?optionally matches any whitespace character
\d{3}a digit, repeated exactly 3 times