David and Emma have been living together as a couple for 20 years

David and Emma have been living together as a couple for 20 years. They have a daughter, Fiona. They are not married.
David runs a small but rather successful second-hand car dealership which he started before he met Emma. When she had Fiona in 1995, Emma quitted her job as an office clerk and stayed home to look after Fiona.
The house they live in was bought in 1996 for 50,000. It is registered in Davids name only. The deposit of 5,000 was paid out of Davids saving. The rest of the money was borrowed from a bank, secured against the house. The loan was paid off by monthly instalment in the next ten years out of Davids income from his business.
In 2001, Emma decided to return to work. She could not find a job she wanted for a few months, and eventually decided to help David in his business. She worked as his office manager. She does not receive a regular salary but had several bonus payments along with other staff at the company whenever the business was doing well. David repeatedly assured Emma that she will always be looked after whatever happens. She never had much faith in saving anyway and most of the money she had were spent on Fionas education, family holidays, cars and other nice things in life.
The relationship is now at its end.
Advise Emma as to whether she has any proprietary claim in the family home. How much would she be entitled to?
Would it make any difference if she paid 500 of her bonus towards one mortgage loan repayment in 2003, when David was abroad on a business trip? If she has any claim, how much would she be entitled to?