I'd imagine it simply the fact you'd taken out £7K in a monththat they barred you other than anything else.
What sort of percentages were they settling XSP at ? Were they keeping as close to 100% or were they publishing overbroke/overround books at times?
The purple place, the most viable alternative to the Betfair exchange
Ok, so this paragraph from their FAQs implies that they guarantee the minimum liabilities with their own money:
How is XSP calculated?
XSP is calculated by Betdaq based on the prices and volumes matched in the exchange market on an event. Betdaq does not publish the XSP calculation algorithm and may adjust it from time to time without notice.
How much can I bet at XSP?
The amount that you can stake at XSP is ultimately determined by the volume of XSP backers and layers in the market however to ensure that customers can use XSP with confidence Betdaq will guarantee XSP liquidity to certain amounts at our discretion.
UK Racing win markets - Layers liability of £3000 per market (or currency equivalent)
Irish Racing win markets - Layers liability of £1500 per market (or currency equivalent)
These amounts are subject to change without notice and Betdaq reserves the right to remove XSP bet permissions and/or cancel XSP bets from customer who are deemed to be abusing these guarantee limits either alone or in conjunction with other customers.