I don't know what の頃【ころ】 means in this sentence. I know ころ means 'about' or 'around' but I still don't understand its use here.
ロンドンに来たばかりの頃【ころ】、私は「Chip Butty」を知りませんでした。
My best translation:
I've just come back from london and I didn't know what a Chip Butty was.