It's all in the history books.
If you look back to the 1970's the original concept for the aircraft was done by Hawker Siddeley at Hatfield hence the type designation HS-146. This followed on from their earlier 3 engined type HS-121 Trident (Sorry to use the T word!). At the time there were no power plants of sufficient thrust that were light enough or quiet enough. Imagine a couple of Spey's roaring into LCY!! So a newly developed mini fan jet was used, but they had to fit 4 to get enough puff.
As the market was not yet mature enough the project was put on hold for a few years until Bae was created so when launched the aircraft became the BAe 146. It only became an Avro when production was moved to the Lancaster factory at Woodford (WFD)
When Avro's planned the upgrade to RJX they did produce some twin engined studies but I'm pretty certain none flew....