Court of Protection Surety Bonds
I am afraid you are unlikely to find another company other than Aviva.
Both my parents had dementia and lived with me until they died. After their deaths, I discovered that their solicitor/deputy had acted negligently and had seriously overcharged them (her bill was £19,000 for one year, plus other charges, even though she carried out no legal work, ignored all court instructions and failed to declare all their accounts). I challenged her bill in court and it was reduced by £6,000. (She had charged for her secretaries, calling them Legal Executives, and had breached other costs rules).
I then obtained evidence of negligence from her files (a very difficult process), and submitted a claim (for c. £22,000) to the Court of Protection for forfeiture of my parents' bonds. The claim included the costs/losses of challenging her bill in court. In total I submitted 556 pages of evidence.
The court dismissed the entire claim in one sentence!
For 2 years I pressed the Court to publish the judgment in my parents' case, since it substantially changes the terms and conditions of the bonds. In particular, it shows there is no point in challenging an abusive bill, since it will cost more to challenge it, than any reduction you are likely to achieve. (In my parents' case it cost c. £7,000 to have the bill re-assessed and reduced by £6,000).
I had also claimed for losses caused by the deputy's failure to obtain Pension Credit for my mother, for her failure to comply with court instructions for one year (to market my parents' property and prepare a Declaration of Trust), for failing to declare 4 accounts belonging to my parents and to account for £2,000 withdrawn from one account during her deputyship), for failing to comply with mandatory panel deputy rules and for charging for non-fiduciary duties.
The Court's Senior Judge dismissed all claims, ruling that, because I had complained about the deputy in the past there was no need to investigate my claim, even though in the intervening years I had obtained incontrovertible evidence. (He also 'forgot' the rules, claiming that bonds were cancelled as soon as a client died or the deputy ceased acting, when this is not the case).
The Court eventually published the judgment, but has refused to inform its clients of changes to their compulsory insurance, as ruled upon in my parents' case. As a result, vulnerable clients are being made to pay for an insurance which does not deliver in the case of professional deputies. (The judgment can be read on the Bailli website, under England & Wales, Court of Protection, January 2013, Letter 'C').
I carried out much research into the bond scheme, and discovered (under Freedom of Information requests) that the bonds of only 4 professional deputies (usually solicitors) have been called in by the court in 27 years! All 4 judgments in these cases were kept secret and have never been published.
The bond does appear to pay out on a fairly regular basis in claims against lay deputies (usually relatives), but the judgment in my parents' case is the first ever published judgment in a case involving a solicitor.
I have a lot of information on the bond scheme, and have written a Case History to help other carers/litigants in person, who find themselves in a similar position.
As far as I can tell, Aviva have a 'monopoly' on this insurance and deputies are always pointed in the direction of Deputy Bond Services, who administer the scheme for Aviva.
Hope this is of help.