My Deaf client lip reads very well. Isn't that enough?
Lip reading is very tiring and extremely difficult. Whilst a person may be able to lip read you for a short time in non stressful situations on a one to one basis, lip reading may become impossible when not in these situations. If a deaf person has requested that you book an interpreter, it is probably because they are finding lip reading difficult and recognise they need an interpreter. Lip reading is also very much a guessing game as only 30 – 40% of words in the English language are distinguishable by lipreading. This means that up to 70% of what you are saying to the deaf person is not actually lip reading – but is guessing' based on the 30% they are lip reading.
Lip reading is a very tiring way of receiving information in a one to one situation (eg: appraisals or interviews), even with a person that is aware of clear communication tactics. Many people can speak up to 200 words per minute (http://www.lipspeaking.co.uk/fact_lipspeaking.htm). In small or large groups (eg: team meetings or training courses), it is impossible to follow what is happening by lipreading alone.
Although the deaf person may seem to lip read very well, on what basis are you making this decision? Just because they may have hearing aids, this may not help them with reception of what is being spoken, depending on their level of deafness.
Give that person a medal, please. There has been many a time when somebody has come along and just assumed that because I can lip-read a small number of very clear speakers for a very limited period of time, that somehow 'carries over' as the ability to lip-read anybody for any length of time.
Lip-reading is the love of oralists, not of mine. To me it is like tea-leaf reading or astrology or pin the tail on the donkey.