Congratulations; you've discovered Daylight Saving.
GMT (more precisely, UTC) doesn't do Daylight Saving. Local time does. And you're in Milton Keynes? British Summer Time is UTC+0100?
Collection Form....
<input type="hidden" name="date" value="<?php echo date("D, d M Y H:i:s"); ?>" /></p>
(Using server local time instead of UTC, 'cos that's what the DBMS's NOW() uses unless you can specify UTC there as well...)
Output page...
<?php {echo $_POST['date'];} ?>