Definitely Hebe and if it isn't salicifolia, it is almost certainly a
hybrid with that species in its recent background. The trouble is
that many Hebes are highly promiscuous and interbreed freely,
resulting in a mess of hybrids that are a devil to nail a definitive
ID. They also seed quite freely and volunteer plants are not uncommon
so un-named hybrids occur with regularity. A picture of the plant in
flower might help, but there's a few months to go before it
performs.