Business Asset

Essentially yes, but...

...the "practice" itself is not an asset , it's a collection of assets, the largest of which (and hence your main concern) is probably goodwill. Other assets will include working papers and perhaps furniture, computers, software, maybe even premises.

In order for an asset to be a business asset at any time, you need to determine that the asset was "being used ... for the purposes of a trade carried on by an individual or a partnership of which an individual was at that time a member" (para 5(1A) of Schedule A1 of TCGA 1992). I think goodwill and the other assets I mentioned fit this description and so are eligible.

In order to calculate the BATR, you need to know the periods for which each underlying asset (most particularly the goodwill) was a business asset.

I would expect that the goodwill has existed and been "in use" as a business asset for as long as the practice has existed (albeit that its value has probably grown over time), and so you should get BATR for the full period of ownership. But some of the other assets may have been added to the practice over time and so may not qualify for as much taper. You should also consider whether some assets are chattels and therefore exempt under s.262 TCGA.