I deal on a daily basis with TWOV and DATV issues for Ghanaian pax transiting the UK. Bottom line is that with a transfer of airport involved, most airlines will not even accept you on the first leg without either a visa or local ALO clearance.

Also, I'm curious which airline departs Gatwick for Ghana at 7am? I'm extremely familiar with this market and I'm unaware of anyone who flies an early AM departure. Ghana International Airlines flies at 1055am from Gatwick - and if you are flying on that flight, please contact me via private message and I can advise specifically about your particular case.