I'm testing Alpari UK ECN for the last week or so. Their DOM constantly shows like 20MM+ depth 6 levels each way (levels are in decimals so it's 0.6 pips distance from the best price)... Not sure how "real" that liquidity is, but certainly looks good.
If you ever have to manage the execution of a 50mm sized order that MUST be done within a few seconds then you'd understand how ONLY a pip or so of slippage is ok (in fact, rather good all things considered.)
He should have multiple accounts at ECNs like IB... And get this done with close to zero slippage. It's not a static market... Where you are forced to take what you see. You should have enough Automation... To trade into positions like this efficiently over a few minutes... Even show a profit with good Algos. If "it MUST be done within a few seconds"... Then it must be a fast market and not doable without big swings anyway.
SWFX consistently has like 200MM of EUR/USD per side not further than 1 pip away, should be way enough for nearly everyone.
The attachment shows insidebid-ask Qty = 50 for EUR.USD at 0.3 pip spread. What is 50? It cannot be 50 million and it cannot be 50,000 USD. Is it 50 retail lots - One retail lot is 100k, so 50 retail lots = 5million USD. This kind of feels right. I checked with a friend of mine who trades fxoptions inter-bank and asked him what kind of spread he will pay on a 100million EUR.USD spot order. He said he has never traded that kind of size (he has been trading for last 6 years) and he guessed between 5 to 10 pips. I asked him for a specific answer and not a guess. Then he went and asked an interbank counterparty for a quote on 100 million EUR.USD and was shown a 6 pip spread from Deutsche and 5 pip spread from JPMorgan. This was during Asian hours, he guessed if he goes and asks during London/NY hours, maybe he will get a quote with 3-4 pip spread on 100 million notional. What is SWFX - I highly doubt 200million size on EUR.USD at 1 pip spread - given what my bank friend told me. We just had this conversation last week - so the information I am presenting is uptodate.
Dukascopy offers access to SWFX pool. I witnessed around 200mm each side there myself during the most liquid hours (Europe/USA overlap).
Actually, it's even worse. LMAX round lots are 10k each on their MTF. So 50 == 500k I don't think general members on their MTF (the LPs) want to post bigger size since there's no last look feature for them to reject a trade should the market snap against them.