Upvote:1
The Direct Airside Transit visa will not allow you to pass immigration or change airports. Only some nationalities require such a visa to transit the UK airside (not passing immigration); many others can transit the UK airside without a visa.
If you need to change airports, the Visitor in Transit visa will allow you to pass immigration to get a hotel and/or change airports. Your onward flight must depart within 48 hours after you arrive (the UK does not operate exit immigration controls at airports; your departure is recorded for immigration purposes when your plane departs with you on board).