Entrepreneur's Relief on part disposal of business property

Client was a sole trader for many years and has now taken on a partner as part of their process for their withdrawal from the business as retiring in 18 months time.

Considering selling half of the business premises to the new partner now and the 2nd half in 18 months when they retire in order to take advantage of two CGT thresholds and to ease the new partner into premises ownership.

My worry is that entrepreneur's relief will not be available on this initial part disposal.  The legislation appears to me to be rather grey as it indicates that entrepreneur's relief is available on a part disposal as part of the withdrawal from a business.

I have just read an article stating that entrepreneur's relief is only available on the sale of the business property if the owner is leaving the business also.

My thoughts are that this initial part disposal of the premises is part of the client's withdrawal from the business, or am I pushing the boundaries too far.

Any thoughts appreciated.