Help with camera lenses

Have canon DSLR & looking for good zoom lens that will enable me to take photos of birds and wildlife.

Have been told Canon 100-400 4.5-5.6 L is lens is fine for most things without spending £1000's of pounds.
Has anybody had experience with this lens and would you recomend this or any alternative.

Also considering canon 400mm f5.6 prime lens,have heard this lens can produce sharper images...
Shall be using tripod most of the time...will i gain with (is) on the 100-400 lens.

Any advice would be great..

Thankyou