Before you send anything along these lines have a think about what you want to achieve and be prepared to be very unpopular for a bit... Also you "independent advice" is us on here but they don't need to know that.
They should treat a letter like this as a grievance without you having to specify it should be treated as a grievance which means you would have a right of appeal if you do not agree with their decision and any resulting resolution. You may wish to spell out that it is a grievance by putting that in.
Can you check the details thoroughly and if anything doesn't look quite right let me know. I'm working from both your threads and the information is quite spread out. I'm also not a lawyer - I'm an HR consultant - but this should be good enough for a grievance so long as the facts are correct. Hopefully some of the board regulars will cast an eye over to check I haven't made a silly mistake.
If you do not get the result you want (ie they say you were wrong and offer you a settlement to resolve this) then you will have to make a tribunal claim if you wish to pursue the matter further. You have a limited amount of time to do this, specifically 3 months less 1 day from the date you receive their decision. You would do this by completing an ET1 form and you can do this yourself or use a solicitor. There may be an issue with the government regulations not being available but you can still put in a claim.
Dear [employer name]
It has recently come to my attention that my holiday entitlement has been incorrectly calculated and that I have suffered a detriment as a result. I have tried to raise the matter informally, as is my preferred method, but this has not led to a satisfactory resolution, so I now request that you review the matter formally.
I have taken independent advice and I understand that the current arrangements, as I understand them, breach the following Acts: The Working Time Regulations 1998 (specifically The Working Time (Amendment) Regulations 2007); The Part-time Workers (Prevention of Less Favourable Treatment) Regulations 2000; The Equality Act 2010; and The Employment Rights Act 1996.
Full time employees are on holiday for 13.04% of their contracted hours per year. As a part time employee I should also be on holiday for 13.04% of my contracted hours per year. As I am required to be working (ie not on holiday) for 40 weeks per year this means that I should be employed for 113.04% of 40 weeks to receive the correct holiday entitlement. This works out at 45.016 weeks paid per annum to allow for the one day of holiday that falls during my 40 working weeks.
I should be paid for additional weeks on top of the 40 weeks to reflect my holiday entitlement. By my calculations this should be an additional 5.016 weeks (less the one bank holiday, May Day, that falls in my 40 working weeks) based on the fact FTE employees get 30 days holiday per annum. However, according to HR I have only been getting 4 weeks which is 1.016 weeks short. I understand this failure to pay my holiday allowance correctly is an unlawful deduction of wages as per The Employment Rights Act 1996.
I have been informed by HR that the calculation they have used which only gives me 4 weeks of holiday is worked out as follows: 40/52x22 (22 being the FTE holidays) = 17 days. This is incorrect because it does not give me the same holiday entitlement to start with as a full timer - which is a breach of The Part-time Workers (Prevention of Less Favourable Treatment) Regulations 2000. It also does not give enough holiday to comply with The Working Time (Amendment) Regulations 2007 which have required all employers to give full time employees a minimum of 5.6 weeks holiday per annum since 1 April 2009 with those weeks pro rata'd for part time employees.
It has also come to my attention that full time employees are benefiting from additional days of paid holiday over the Christmas/New Year period. As a part time employee I am excluded from this benefit and understand I should be receiving a pro rata'd benefit to ensure The Part-time Workers (Prevention of Less Favourable Treatment) Regulations 2000 are complied with, but also that failure to give equal benefit to me as part time worker is potentially indirect sex discrimination as per The Equality Act 2010. I understand I should receive 87% of whatever benefit full timer employees received because my employment contract should be for 45.016 weeks compared with 52 weeks for FTE employees.
I therefore request that I am compensated for the additional leave that should have been paid for the last X years plus interest. I have worked it out using the weekly rate of £337.31 because there are 52.177457 weeks in a year and FTE salary is £22,000 per year and my working week is 0.8 FTE. This is £342.71 (1.016 weeks holiday) for each year which means I have been underpaid by £XXXX over the last X years.
I also request that I am compensated for any additional paid holiday that has been given to full time employees over the Christmas/New Year period.
Yours sincerely
Shoppaholic