Anyone used Wyeast 1335?

I've been tasked with brewing an Adnams Explorer clone for a wedding. Have got all the malts and hops and got a smack pack of 1335 (British Ale II) which Google suggests is the best yeast to use.
I'll be brewing a 50 litre brew length so chucked the smack pack into a starter 5 days ago to bulk it up a bit...the results have been underwhelming.
Haven't really seen any visible fermentation, no krausen. It did seem to get a bit murkier and having put it in the fridge to settle there's a decent layer of yeast at the bottom of the flask so something does seem to have happened.
I'm going to chuck the yeast into some fresh wort tonight to see what happens but I'm not convinced that I want to trust 50l of wort to this yeast at the moment. I have enough dried Nottingham for 50l and right now I'm inclined to use that.
Has anyone used this yeast before? Is it a quiet fermenter or do I have a dodgy pack.

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I think some liquid yeasts do better after stepping them up a couple of times - Wyeast Scottish Ale yeast was similar to what you describe but was much better after two starters (2L then 5L).

That's very much what ended up happening. Went into a fresh 2l and went normally. Then allowed to settle and put another 2l in and it went again. Pitched into 50 litres and was going within 5 or 6 hours.
So either it needed stepping up as you say or it didn't like the heat, the first starter was on those couple of 30C days we had, things had cooled down by the 2nd starter.

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I've read from a few different sources that liquid yeasts tend to do better on the 2nd or 3rd generation - that is certainly borne out by my own experience.