a UK version of Germanwings
That's very hard as 4U is effectively the German version of Easyjet. When 4U was founded by LH in 2002, there were big gaps in the country's budget airline market. It was formed to counter EZY and FR expanding in Germany, which has mostly worked. EZY has a few strong-holds (e.g. SXF), but they are way below what they could have been. Same for FR, which is even partially moving out of Germany. The UK is a saturated market, there is just no space for WW outside a few niches, really. And needless to say, 4U has seriously more modern planes. I'm happy though they've resurrected EMA-CGN, which I thought wasn't making money. Making EMA-GVA more frequent I think would be a safe bet, maybe even a weekend BHX-GVA in summer. I'm not living in fairy-tale land, so shouldn't suggest BHX-SXF or BHX-CGN ('the cursed route').