According to Tannoy, you should use power amplifier from 50-500w. You can download information about Arundel on the link:

http://www10.plala.or.jp/minmin_house/brochure-arundel.PDF

You could get by with a 20 watt amplifier if you had speakers with a sensitivity of 95 db/watt or higher. Unfortunately, very few speakers are that sensitive. Yours are fairly sensitive, however. It might work.

I would suggest an amplifier that has at least 60 watts per channel.