Maybe his name is Alexei, but Petrov is not his family name, and he certainly isn’t just any old Colonel. But he’s not going to tell us. All we find out about him is that he is certainly related to the Russian Imperial family, and is probably a Grand Duke at the very least.
He is the Russian link who is responsible for bringing Brian and Harry to Russia, where they can work on the Netopyr (and also on the Zaamurets). In his capacity as the director of the Imperial Army proving ground at Kubinka, he is responsible for sorting out some of the oddball ideas that are put forward and consigning them to the relevant areas. Note that in real life, Kubinka only became the USSR tank proving ground in 1931. I have decided that it would make a suitable test area for Imperial Russia as well, and moved the time forward.
He is the daughter of Maria, who was educated at Cheltenham Ladies’ College (as, in real life, were German Admiral Tirpitz’ daughters).