The British actor was attending a pre-BAFTAs dinner in London Tuesday -- where, upon exiting, the dude came across as sharp and ready to mingle ... dressed to the nines in a tux and rocking a sly smile that telegraphed pure confidence.

More interesting than his dapper appearance was who he eventually left the event with ... namely, actresses Ellie Bamber and Saffron Hocking -- who were in the same van he hopped into as they all made an exit.

As Joe piled into the vehicle ... paps fired away, and they happened to catch Saffron grinning wide and eyeing the homeboy here with a good old-fashioned once-over. Indeed ... she seems happy to see him.

From what we can gather ... he's fully moved on from T-Swift and enjoying his life across the pond with other lovely ladies, who just so happen to be in the same line of work as him.

Of course, it's interesting to see JA in such high spirits lately -- especially since Tay Tay is dropping a new album soon that just about everyone suspects will take aim at him and their relationship ... that's what the Swifties are anticipating anyway.

By most accounts, their relationship didn't end all that well ... and considering that Taylor's very much so living out loud -- especially in her new relationship with Travis -- many suspect she's happier and freer than she's ever been ... including when she was with Joe.

In any case ... Joe doesn't seem to be sweating it very much -- he's a man about town!

Taylor, meanwhile, appears all set to dredge up their past anew with another breakup album -- that's what looks to be promised, at least. Her fans eat that stuff up -- but it's a little weird ... especially since she's knee-deep with a whole new boyfriend now.