express visa in London?

Hi,
I have made a last minute decision to join some friends in Ghana but as far as I can see there is no way to get an express visa in London (unlike the US). I was hoping to fly out next Thursday, but am a bit worried about booking my flights as necessary to get a visa when the minimum processing time is 4 days. Does anyone have any advice as to if there is any quick way to get a tourist visa in London, or if it takes a lot longer than four days?
THanks

Looks possible from what I found. The Ghana High Commission in London will do it. They say they you need some extra time, and then say around 2 hours! That ain't bad at all. See below:

TOURIST VISA

DOCUMENTS
All visitors to Ghana must be in possession of a valid passport or legal travel documents.

All visitors entering Ghana must have valid entry visa or, in the case of Commonwealth nationals, entry permits, issued by a Ghana diplomatic mission or consulate abroad or any other visa issuing authority mandated by the Ghana Government to act on its behalf.

ECOWAS nationals and those of other countries with which the Government of Ghana has specific bilateral agreements are exempted. Travellers are strongly advised to ensure that they have all the necessary documents before arriving in Ghana.

Check well that your passport will not expire within six months of your intended departure date.

Valid certificate of inoculation against Yellow Fever will be inspected at point of entry.
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YOU NEED :

2 PASSPORT PHOTOGRAPHS

30 - 70 POUND`S

2 ADDRESS REFERENCES in GHANA + NAMES A N D PHONE NUMBERS

AND YOU WILL NEED TIME ! ( UP TO 2 hours )

MAXIMUM : 2 year - VISA ( MULTPLE VISA )

http://ghana-net.com/ghana_high_commission_london.aspx