Review propossed changes to an existing contracts of employment

We have proposed the following contract clause changes to staff in the following way. I would like some advice on the legitimacy of the way we have done it and the enforceability of the new clauses. I have also attached PDF copies of the full contract Word versions are available.

"As per your existing employment contracts, we are making changes to two existing clauses and adding an additional one, these changes will come into effect 08/12/18. Any questions speak to me, please see the below:

Current Clauses

11. Annual Leave

(a) The Company annual leave year is the calendar year from 1st January to 31st December.
(b) Your total annual holiday entitlement in your first completed calendar year of employment will be 20 working days.
(c) For part time employees, whose hours of work are variable each day, annual leave will be calculated in hours and reduced by the amount of hours taken on each occasion.
(d) If you commence employment part way through the Company annual leave year your entitlement will be pro-rated accordingly.
(e) You must not make firm annual leave arrangements prior to receiving confirmation from management that your request has been authorised.
(f) The Company reserves the right to refuse any request for annual leave in the interest of the efficient operation of the business.
(g) No more than two weeks of annual leave entitlement can normally be taken at one time. In exceptional circumstances and at the sole discretion of management, you may be permitted to take annual holiday in excess of two weeks.
(h) You are required to submit a completed annual leave request form to your Line Manager as soon as possible, prior to the annual leave start date and no later than twice as long as requested e.g. for annual leave of 2 weeks you are required to give at least 4 week’s notice.
(i) Payment for any annual leave taken will be at your normal rate of basic pay.
(j) You will, in addition to the Company’s annual leave, be entitled to paid leave on the 8 normal bank/public holidays as per Royal Proclamation.
(k) In the event that you work part time you are entitled to bank/public holidays on a pro rata basis.
(l) You may be required to work on a public holiday.
(m) If you are required to work a bank/public holiday you are entitled to take the day, based on your normal working hours, at another time, as agreed with your Line Manager.
(n) Annual leave may be taken as a half day, with prior agreement of management.
(o) Where a recognised public holiday falls on a Saturday or Sunday, alternative dates will be substituted for these.
(p) On leaving employment, payment will be made for any accrued annual leave entitlement not taken, or, deducted from any wages owing to you for any annual leave taken without accrued entitlement.
(q) The Company reserves the right to require you to take any outstanding leave entitlement during your notice period, whether that notice is served by you or the Company.
(r) You are required to take all your annual leave in the year it is accrued and any outstanding leave may not be transferred into the following annual leave year.
(s) If you are absent from work because of sickness immediately prior to, during or immediately after, a period of authorised leave/bank holiday(s), and your incapacity extends into the authorised leave/bank holiday(s) period, you are required to submit a GP Note covering the period and you will be permitted to take this leave at some other time, as agreed with the management.

21. Non Competition

For a period of 12 months after the termination of this agreement, you shall not solicit or seek business from any customers or clients of the Company.


Amended Clauses (Changes Clauses)

11. Annual Leave

(b) Your total annual holiday entitlement in your first completed calendar year of employment will be 25 working days.
(c) Three of your days holiday must be taken between Boxing Day and New Years Eve, members of the sales team are expected to cover incoming calls, emails and web form sales enquiries.

21. Non-Competition

For a period of 12 months after the termination of this agreement you shall not solicit or seek business, or employment from any customers, prospective customers, associate consultants, suppliers, or UK business competitor of the Company.