PHP to build a UK telephone Regex Pattern from known formats.

uk-phone-regex.php

<?php

// UK telephone formats (ref: http://www.area-codes.org.uk/formatting.php#programmers)
// prefix:chunks (eg. 434 -> 4444 333 4444) - # = any 0-9 digit
$formats = array(
	'1:45',
	'1:46',
	'11:334',
	'1#1:334',
	'13873:55',
	'15242:55',
	'15394:55',
	'15395:55',
	'15396:55',
	'16973:55',
	'16974:55',
	'16977:54',
	'16977:55',
	'17683:55',
	'17684:55',
	'17687:55',
	'19467:55',
	'2:244',
	'3:334',
	'5:46',
	'500:36',
	'7:433',
	'800:36',
	'8:334',
	'9:334',
);

// known phone numbers that do not adhere to the formats defined above
$exceptions = array(
	'800 ?1111',
	'845 ?4647',
);

// compile a regex pattern for each area code format
$patterns = array();

foreach($formats as $data) {
	list($prefix,$format) = explode(':',$data,2);

	// compile prefix regex with known digits
	$format = str_split($format);
	$format[0] = (int)$format[0] - strlen($prefix);
	$prefix = str_replace('#','\d',$prefix) . ($format[0] > 0 ? sprintf('\d{%d}',$format[0]) : '');
	unset($format[0]);

	// compile suffix regex for digits
	$patterns[$data] = sprintf(
		'%s ?\d{%s}',
		$prefix,
		implode('} ?\d{',$format)
	);
}

echo '<pre>',print_r($patterns,1),PHP_EOL,PHP_EOL,implode('',array(
	'/^(?:\+44 ?|0)(?:',
	implode('|',array_merge($patterns,$exceptions)),
	')$/'
)),'</pre>';