The draft Statutory Shared Parental Pay (General) Regulations (the general regulations), the draft Shared Parental Leave Regulations (the leave regulations) and the draft Maternity and Adoption Leave (Curtailment of Statutory Rights to Leave) Regulations are seen as the core set of regulations for the regime (see box "Useful links"). Although in all, around 19 sets of draft regulations are planned.

Together with about 36 pages of the Children and Families Act 2014 (and that disregards the pages of amendments that do little more than facilitate the exercise of rebranding paternity leave) these draft regulations set out the legislative provisions that seek to deliver on the changes announced in the government's November 2012 response to the modern workplaces consultation (www.practicallaw.com/5-506-6385).

SPL and ShPP are due to start from 5 April 2015 for children expected to be born or adopted on or after that day. Placements under "fostering for adoption" schemes and surrogacy arrangements that use parental orders are included in the scheme.

Six months earlier, from 1 October 2014, the related protection against dismissal or detriment for making or proposing to make use of the new system is due to start.

In contrast to the opacity of the draft regulations, which with so many moving parts can be likened to playing four-dimensional chess, the core of the government's proposals is straightforward. Starting with what stays the same, there is no change planned in the current rights to two weeks' paternity pay. Nor to the separate right to up to 18 weeks' unpaid EU parental leave (although the age limit of the child will increase from eight to 18 years from 5 April 2015).

On statutory maternity rights, the default position remains the same as the current one: a woman who qualifies for statutory maternity leave and pay can still take her 52 weeks' leave and 39 weeks of maternity pay. That entitlement remains the maximum. However, the proposals permit that maximum to be split between the maternity system and the shared parental leave system.

If the woman gives up some of her statutory maternity entitlement, that element, whether pay or leave, can transfer to the equivalent part of the new system, as appropriate. This also applies to state maternity allowance for self-employed women and recently employed women who are excluded from statutory maternity pay.

For a self-employed woman with an employee partner who meets the qualifying conditions, a notional 52 weeks' leave (less the weeks that are paid as maternity allowance) can be transferred to SPL. Her partner can also get the unpaid balance of weeks of maternity allowance as ShPP.

Statutory adoption leave and pay is treated in the same way. The current additional paternity leave will be abolished and instead the equivalent right becomes part of the SPL system.

To get access to SPL and ShPP, each parent or prospective parent must meet employment and earnings and other qualifying conditions. However, statutory maternity and adoption leave for a mother, as at present, remain a right from day one.

Subject to ring fencing the two weeks after birth (four weeks for certain factory workers), the woman and her partner can decide to share between them the balance of her statutory leave and pay. This can be done in minimum periods of a week in any combination and at any time, but only during the 52 weeks after the date of birth, application for a parental order, or placement for adoption. An employer's agreement is required if the pay or leave is broken up into separate blocks of weeks, rather than running for one continuous period.

As ShPP is to be paid at the flat rate of statutory maternity pay (SMP), it is likely that most couples will choose to forgo no more than 33 weeks of SMP. The first six weeks of SMP is paid at 90% of the woman's pay if that is higher than flat rate SMP. If she takes less than six weeks, the balance of the higher rate is lost.

The couple may take the weeks of leave and pay at the same time, overlapping, or one after the other. They can take it in blocks, breaking it up with planned weeks of work. Each also has 20 "keep in touch" (KIT) days available to use during a period of ShPP or SPL. Although KIT days cannot extend the period of leave, they can be used to supplement the low rate of ShPP, or to try out patterns of part-time work. As with the current KIT days, pay and the nature of the work to be done are both matters to be agreed.

The possibilities are exciting. They also call for careful planning by employers and employees alike. For employers, the change is likely to require more than just refreshing existing policies. Is it feasible to offer suggested patterns of leave broken up into separate blocks? What criteria should be applied? How are competing requests to be dealt with? What about changes of circumstances?

For employees, the notice requirements are exacting. The leave regulations limit an employee to two variation notices for SPL. Although no limit is given in the general regulations for ShPP changes, entitlement to pay depends on being in a period of SPL. The draft regulations have to be read and understood together. The idea is that they should work as a harmonious whole.

A pattern of SPL and ShPP can be planned well in advance. An obvious point is to provide employers with details along with notification of the date from which it is intended to take maternity leave. Each parent must notify their own details to their own employer. The intention is that the two employers will not need to liaise at all.

The details can be varied by a further notice that does not need the partner's consent if the change is notified at least eight weeks before SPL and ShPP start. For any later change, the draft regulations require a partner's consent to a change. As with the initial notification, if the request is for separate blocks of leave, rather than for a continuous period, the employer has the choice of consenting to the leave dates, suggesting alternative ones, or just refusing. ShPP can only be paid during a period of leave, so there is no repetition of this provision in the general regulations. If the employer refuses, the fallback is to withdraw the notice (relying on the previous one) or, subject to some extra notification conditions, switch to a continuous period.

Unexpected circumstances, apart from death, have not been taken on board. Incapacity or estrangement may delay or prevent obtaining a partner's consent, and having already given two variation notices would prevent a third one being made. Unless some failsafe provision is made, a parent could end up with fewer than 33 weeks of SMP and ShPP.

Some glitches are apparent in the draft regulations. Their complexity does tend to inhibit understanding, making it important for employers to plan well ahead for the changes. It is reassuring that BIS is working on a wide range of secondary materials for information and navigation. Online tools, hopefully solving that four-dimensional chess problem, are also planned.