Gamal Yafai is competing in his first major senior tournament
Great Britain are guaranteed their most successful European Championships since 1961 after three more boxers won their quarter-finals in Moscow on Wednesday.
Bantamweight Gamal Yafai joined his brother Khalid in the semis, as did lightweight Thomas Stalker and Welsh bantamweight Andrew Selby.
All four fighters, plus featherweight Iain Weaver, will box for final places on Friday.
"What they've achieved is phenomenal," said head coach Rob McCracken.
"We've got a young team and this is regarded as the toughest tournament in amateur boxing. It is a great boost for our hopes looking ahead to London 2012.
"It is going to get much harder on Friday but the lads are so full of confidence and they have all come on so well in training over the last few months."
The last time GB won more than two medals at the tournament was in 1975, and the last time they won five was in 1961, when the final tally was two gold and three bronze.
Birmingham's Gamal, 18, pulled off an upset win over Ireland's 54kg World Championship bronze medallist John Joe Nevin.
A superb display of counter-punching saw him breeze through 7-1 to join flyweight Khalid, who made it through on Tuesday.
Gamal said: "It's the best feeling ever to have guaranteed a medal in my first major senior tournament but I'm going for a place in the final and gold now."
Behind the scenes with Britain's top amateur boxers
Potentially Gamal could meet his team-mate Selby in the final after the Barry boxer beat Turkey's Furkan Memis 4-1.
Liverpool lightweight Stalker survived a countback scare to edge Latvia's Artjoms Ramlavs.
Stalker was not in the same form as he had been beating reigning world champion Domenico Valentino last time out and admitted he may have approached the fight feeling a little over-confident.
Stalker, 25, said: "I looked at my opponent and thought he wouldn't be too strong but he was better than I thought.
"But I got through and it's a great feeling to get a medal. I'm so happy to finally get a bit of luck.
"The confidence in this team is great. We have a real winning mentality. We used to walk past other teams like the Russians and fear them. Now it is the Russians and the rest who are fearing us."
However, there was disappointment for Liverpool light-flyweight Tommy Stubbs, who was comfortably beaten 8-1 by Belfast's Beijing bronze medallist Paddy Barnes.
Meanwhile, Ireland lightweight Eric Donovan beat Hungary's Miklos Varga, meaning Ireland, like Great Britain, have five boxers guaranteed at least bronze medals.
Tyrone McCullagh - who next meets Weaver - Darren O'Neill and Ken Egan all made it through on Tuesday.