The Euro didn't exist and the 70's started under the Bretton Wood's agreement. It wasn't until '76 that countries agreed to a floating currency. I don't think London's ability to influence a basket of mediocre pegged currency's gives us any insight into their ability to influence the Euro.

I don't think you understand what EuroDollar means...

https://www.investopedia.com/terms/e/eurodollar.asp

No, I know what the eurodollar is. The power of London over the "eurodollar" at the time was that the businesses and banks in Europe were doing business locally in their domestic currencies (eg Italian Liras) which did not have any international clout. These businesses and banks were effectively forced to go through London Eurodollars to operate internationally to minimize risk. With the introduction of the Euro, none of that matters anymore and London has no power.