The factors affecting the planning permission entail:

Neighbours: It's possible that your neighbours are just as worried about work that may negatively impact them as you are about modifications that could negatively impact how much you enjoy your own home. For instance, your construction project may obstruct their windows’ views or take away part of their light.
Design: Individual preferences differ, and distinct designs are appropriate for various kinds of properties. Nonetheless, you and your neighbours are probably going to find a well-designed structure or addition to be far more appealing. Also, when you decide to sell your home, it probably will be worth more. It is vital to consider carefully how your property will seem once the remodelling is completed.
Nature and Wildlife: It could be necessary for you to think about how any work you want to do would affect animals. Some animals, plants, and ecosystems can be protected by national laws (such as badgers), the 'Wildlife and Countryside Act 1981', or by-laws from other countries (EU-protected species, such as the Great Crested Newt). The Local Planning Authority and Natural England can advise on what types of species and their habitats are affected by such projects.
Environmental Health: Some development projects may cause air pollution, unfit housing problems, unhygienic food preparation etc. requiring an ‘Environmental Impact Assessment’. The assessment's purpose is to consider the environmental impacts of development. Its job is to supply local authorities with sufficient data on an area's environmental effects to decide whether to approve planning permission.
Roads and Highways: The local highways authority is in charge of roads and highways, and they must be contacted when construction activity affects or changes the condition of a roadway.
Fire Safety: Regarding their Planning Gateway One service, the Building Safety Regulator (BSR) and the Health and Safety Executive (HSE) offer guidelines. The advice is meant for applicants, experts, and local authorities involved in the planning, design, and approval of high-rise residential and educational structures concerning fire safety.

What factors can affect the planning permission?