Attempting to get the first Monday of the first Week of the month. May 1st is a Sunday therefore the previous Monday is expected to be the first Monday.
$date = '2016-05-01';
$dateTimeObject = new DateTime($date, new DateTimeZone('Europe/London'));
$dateTimeObject->modify('first monday of this week');
echo $dateTimeObject->format('d');
However this echos 02 which is the following week's Monday when it should be April 25?