Share premium value, then hive up to Holding co

Hi,

Client had initial investment in trading co A - £ 150k for shares. One year later, holding company- B set up and share for share exchange agreed, therefore Holding co now only shareholder of trading co A

Further investment sought in Holding co  circa £ 350k.

My question is - what happens to the initial £ 150k sitting in Share premium on Trading Co A Balance sheet - should this be moved to amount owed to Holding Co, with the contra in the Holding co, or left as it, or indeed written off.

( Irrelevant, but all investment will be lost eventually as company no longer viable)