UK in Autumn has bad weather but not so bad that you will not fir in 45 hours of flying in four months.
The good news is that you will be doing your initial flying in September when the weather is not so bad - quite summer like - if you are doing a career/intensive course and work at it six days a week I would think you'd be able to fit in 45 hours in September.
Of course it may take you longer than 45 hours to complete - age seems to be an issue - someone once told me to add an hour for every year over 18 - from personal experience and asking around it seems to be a good rule of thumb.
Your end of the year target seems easily achievable if you work at it - it may be the exams and book work that slows you down as much as the UK weather (I now live some where sunny where an ICAO PPL can be obtained in 35 hours but am not so sure that weather is the real problem - people who go to another country to do their PPL or a "far from home" residential course just get it done quicker because there are no/fewer distractions as much as the weather conditions).