It is unlikely that there is any flexibility with the employer's terms and conditions unless stated in the vacancy advert. The best attitude is to place trust in the employer's offer and to only apply for jobs that offer satisfactory pay and working conditions.
Contract negotiations mostly apply to highly skilled and highly paid jobs. The applicant will need to justify his/her salary demands by demonstrating that they are in accordance with market rates and their skills and experience. You can ask for a pay rise after working for a company for a while, if your pay appears to be out of line with employees doing similar work. You will normally have an annual pay review. Holiday pay is included and remuneration is usually expressed as an annual gross salary. Trade jobs, e.g. carpenters and bricklayers, often show wages as hourly.
The most common non-statutory benefits are: flexible working arrangements; private healthcare or healthcare insurance; subsidised travel; London weighting (extra pay if working in the capital compared to the national average); use of a company car; subsidised meals at an office canteen; subsidised membership of a gym or club; pay bonuses.