Usually combine my Avios doesn't count as activity as you could keep accounts alive just by moving Avios back and forth between BA and Iberia.

I think they made an exception for transfers from bmi though as miles earned through bmi were miles earned by the credit card and you couldn't just transfer miles back and forth between bmi and BA to keep the account live.

However, if you are worried, it wouldn't do any harm to do the occasional online purchase through the BA estore. This definitely extends the validity of miles and your purchase can be something like a couple of iTunes. Some of the estores ignore VAT when calculating your bonus so you should make sure your purchase is £1.20 or higher.