I make Curry Katsu and the Katsu sauce I make is VERY similiar to Hela's Currywurst sauce.
No exact measurements but this is how I've done it time and time again:
5 tbsp (heapful) of Tomato Katchup (Morrison's own brand)
1 tbsp of Soya sauce
Half tbsp of Worcester Sauce
Half tbsp of Mirin (Rice wine + Sugar/Corn Syrup if you don't have it)
Big pinch of ginger powder
Then finish with 1 tsp Garam Masala (specifically Morrison's own brand as different make have different ratio of spices, this is what I use, tried Swartz before and it bombed)
Give this a good mix before dinging it in the microwave, High for 1 minute
(I cover with cling film but poke a hole to ease the steaming)
Mix well again before resting for around 30mins / cool before using.
This gives 1 portion and I've scaled up as high as 4 portion. Add 30secs in microwave for every increase in portion.
Or you can do the German thing and buy bottles of Hela for your dose of currywurst.