Dim why do spreadbetters affect the price?
They more than affect the price, they can, to a certain extent, control it, by placing bets which result in very high levels of buying and selling, so driving the price on highly illiquid microcaps.
With a £10k margin (or deposit), you can (if you are stupid and greedy) trade about 200 grand's worth of shares, and that is enough to guarantee the price will rise. You say to the betting company 'go long at £20,000 per point on Zoo' equivalent to the exposure of 2 million shares, requiring £10k margin.
Your spreadbet company will take a day or two to offset that bet, filling your bet as they manage to hedge it, either by buying shares in the market, or by taking out bets or cfds with other bookies (or spreadbet/cfd companies). Note if any are hedged with another company via cfds for example, then that company will lay thay bet off in some way, but it is almost always laid off by a purchase of shares eventually. (With bigger capped companies, the betting company can lay off bets with other betters betting in the opposite direction and accept some risk, but not with microcaps). They make a turn on any bets by hedging at a better price than they give the better.
Obviously, the share buys drive the price up over a period of days. I think big betters rely on this momentum sucking in other punters to drive the price higher still, after which they take their profit and close their positions, resulting, in the example above, 2 million shares being sold over a period of days. Look at Bits for an example of this - if the momentum fades, and the 2 mill isn't bought by other punters, the price simply plummets down (usually)quicker than it rose.
When I bought zoo a few days ago, I thought the betters had already exited, so as not to be exposed to the interims. I now think I was wrong there, and they still had positions to close - hence the drop. I think they have now finished closing.
Note this causes massive price instability, with prices being driven much higher (by buys of £200k) than if the shares themselves were bought (by buys of £10k - the cash/margin/deposit the better has available) and then much lower as the trade is closed.
It's greed gone mad, imo. The stats show that, overall, these betters lose, yet you'll only hear them shouting about their winners. The cost to shareholders of them betting is the massive price swings they cause - totally disconnected to the fortunes of the company.