Children's author Helen Bailey was plied with sedatives and "probably suffocated" by her partner, a court has heard.

The 51-year-old's body was found dumped in a well hidden below her £1.5 million home in Royston, Hertfordshire, in July last year three months after she was reported missing.

The remains of her beloved miniature dachshund, Boris, was found by her side.

Her fiance, Ian Stewart, 56, is accused of "secretly" giving her a sleeping drug in increasing amounts over time so he could murder her for her money.

Opening the case at St Albans Crown Court, prosecutor Stuart Trimmer QC said: "This was a cold-blooded murder - the Crown's case is that ... Ian Stewart killed her, probably by suffocation whilst she was sedated by the drugs he had administered for some time.

"The Crown say this was simply a long-planned, deliberate killing, a cynically executed murder that had money as its driving motive."

On the day she is said to have died, Ms Bailey's bank account was accessed, with a standing order to the defendant bolstered from £600 to £4,000, the court heard. Stewart denied he carried out the transaction.

The former software engineer was in line for a "substantial financial advantage" of around £1.8 million plus the value of the two properties she owned in the event of her death, Mr Trimmer said.

Ms Bailey was said to be worth around £4 million, earning around £5,000 a month in royalties from her books.

She is known by younger readers for her characters Electra Brown and Daisy Davenport, but found a new audience with her blog, Planet Grief, about becoming a widow.

In the weeks leading up to her death, the court heard Ms Bailey was concerned she was feeling unnaturally sleepy.

A statement from her mother Eileen Bailey said: "She would say 'Mum, I don't even recognise my own hands' when she was sitting at the computer."

Mr Trimmer said: "The reason, the Crown says, is quite clearly because she was being fed Zopiclone."

Traces of the drug - which is used to treat insomnia- were found in her body during a post-mortem examination, having been there as early as February 2016.

Stewart is accused of creating a charade Ms Bailey had gone missing - even killing her dog to add to credence to the theory.

He said he discovered a handwritten note from Ms Bailey saying she needed "space and time alone" and had gone to her Broadstairs home.

No note was ever found, the jury heard.

Officers eventually made the grim discovery on July 15 after opening the hatch to the well, which was located under a concrete floor, and seeing an arm sticking out of the waste.

Stewart later told police that two men - named Joe and Nick - were responsible for the killing and the disposal of the body.

He is charged with murder, three counts of perverting the course of justice, preventing a lawful burial and fraud. He denies all accusations.