Spread on stocks.


Could some kind soul with accurate intra-day bid/offer prices help me with this?

I recently had trailing stops on two shares held with The Share Centre trigger sales at prices well below the lows shown on my ShareScope EOD data.
I queried this with Share Centre and was told that the spreads widened enormously for no apparent reason, thus triggering the sale. (As ShareScope shows mid-prices, I couldn't argue with this as a symmetrical large spread would not show up on my data.)

Would someone please tell me if anything strange happened to the spreads on Arriva (ARI) before 9:48 on 24th Jan, and on Punch Taverns (PUB) before 9:42 on the same day.

I have no problem with a protective stop-loss being hit - that's what they're for. What I am trying to find is a confirmation of the Share Centre trader's statement that the spread on this stock widened enormously. Doing the maths, these shares must have moved instantaneously from a .5p spread to around 55p to trigger the stop.

ARI Trades

I got data below off ADVFN – trades- for ARI on 24/1/2005 the intraday on ADVFN only goes back 5 days shame as that shows spreads very well

TIME Qty Price dealt Bid offer Trade type
9:57 300 531 525.5 531 AT
9:49 1000 532.5 504.75 532.5 AT
9:48 302 504.77 503.25 533.5 O
9:48 133 501.92 500.25 533.5 O
9:48 100 533.5 533.75 534.0 AT

It seems that bid price at 9:48 was at around 500, just before and just after it was much higher 525 / 533.
The low of the day on sharescope was 528
The low of the day on Investor Ease was 528.5
So what is going on?
As Sharescope and Investor Ease have slightly different values I assume they have different sources and therefore it is not an error with them.
Is the “mid” or single quoted price of a share always at the middle of the spread
I think I have observed instances of the single quoted value being at one end of the spread rather than in the middle although then the spread was not so wide.

Sharescope just have referred me to stock exchange document quoted below

“3.2.3 High and low prices
We recommend that the highest automatically executed trade price and the lowest
automatically executed trade price, within the official trading day, should be used to
calculate the daily high and low price.
Note, if you calculate the high and low using additional trade types other than AT and
UT, e.g. result of options trades (trade type RO), this should be clearly displayed”

I think that this might explain it , The low priced trades at 9:48 are trade type O (Ordinary trade made through Market Makers) and would fall outside of the stock exchange definition above and would not appear on sharescope
nb sorry about table above it looked all right before I submited it how do I do tables on the forum or how to attach a spreadsheet or word file?
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