Hello Helen. What a fabulous birthday present for your father!
I don't have a service manual for the 10, but my Atlas has almost the same engine, as did many Standard-Triumphs through the 60's and 70's such as the Herald and Spitfire. So, although my Atlas service manual specifies BP 20W, Shell 20W/20 or Esso 20W/30 etc, I have used the same oil specified for the later cars - a 20W/50 motor oil.
But there is something else to consider. All motor oils from the 40's until the 90's contained an additive called ZDDP, but this is being phased out of today's oils as it damages catalytic converters. However, our cars need the zinc in ZDDP as it is an important friction reducer - the cam and followers rapidly wear out otherwise! So you need to look for an oil formulated to the earlier standard. Start by looking for something that says "Classic Motor Oil", or something like that. Then, just to make sure, look in the small print for the API (American Petroleum Institute) rating. You need to see API SF or any final letter through to API SL. It's the SF through to SL that's important as after SL they started reducing the proportion of zinc by reducing zddp.
To summarise, a "Classic" 20W/50 motor oil with an API class of SF through to SL
I imagine the club shop will be able to help you with the oil filter. I hope this is of some help.
I was researching myself on old threads on here and came across some info on the ZDDP so realised it was important to have something that contained it or similar. I will pass this information on to Dad.
I have got a lovely photo of Dad with his Standard, but apparently it's too big to attach to my profile pic