colleagues as refrees

[gbhsmp]

The immigration rules say

section 6.3.7.3
For adult applications each referee should have known the
applicant personally for at least 3 years

Does this mean that office work colleages cannot be refrees ?
Has someone been successful with refrees only as office colleagues ? Both my refrees are from the same office where I worked.
Will this be a problem ?

[sogy]

They can, if they are otherwise qialified (one of them "professional", the other a British citizen of good character and either professional, or > 25 yo)