Nigerian Visa
Basic Requirements 
A Nigerian visa is a permit issued by the Nigerian visa authorities, allowing a person to travel through the country or reside in it temporarily, provided they are visiting for tourism or business purposes. You can apply for your Visa up to 3 months before your intended arrival date.
Please note: Tourist visas are only issued to people who are visiting family or friends.
Country-Specific Requirements 
The only nationals who are excluded from having to apply for a Nigerian visa to enter the country are the ECOWAS nations which form the Economic Community of West African States.  Visitors from these countries are not required to hold a visa when entering Nigeria.
Processing Times
When applying for a Nigerian visa, processing time and fees are very dependent on the visa class, as well as the nationality of the applicant and the time of year.  However, the general processing time for a Nigerian visa is 3-5 working days.
Temporary Nigerian Visas
Nigerian Tourist Visa
The Nigerian tourist visa is issued with a validity of three months, and is intended solely for applicants wishing to visit the country for the purposes of tourism, or visiting friends and relatives.  However, applicants must leave upon the visa’s expiry and must not engage in any form of employment while on their visit.
Additionally, applicants for a Nigerian tourist visa will need to satisfy a number of requirement, including:
Supplying a current and valid passport from their country of residence, with a validity of at least six months from the scheduled expiry of the visa.
nDemonstraing the pupose of the visit, as well as an intention to return to their country of residence.  This can be shown through evidence of a holiday booking and a valid return / onward travel ticket.
nSupplying evidence of an invitation from the hosts, in the case that the applicant is travelling to visit friends and relatives.
Providing proof of sufficient funds for the duration of their stay.
Nigerian Business Visa 
A Nigerian business visa can be granted to foreign nationals wishing to travel to Nigeria on a temporary basis in order to attend meetings, conferences and engage in other business activities.  However, under no circumstances may they engage in any form of Nigerian employment.
The Nigerian business visa is issued at a standard length of 90 days validity.  However, this can be extended, if necessary.  The eligibility requirements of this visa are similar to that of the Nigerian tourist visa, with the additional requirement of a letter of invitation from an acknowledged Nigerian company.
Nigerian Embassy Information
Nigerian High Commission 
9 Northumberland Avenue
London
WC2N 5BX

Telephone:  020 7839 1244
Fax:  020 7839 8746
Website:  http://www.nigeriahc.org.uk/  Source: visabureau.com